Imágenes de páginas
PDF
EPUB

bastardized, that theory being that unripe ova are partially impreg. nated by the spermatozoa of the foreign male, not sufficiently to fully vivify them, the influence of this impregnation affecting only the epiblast, from which the skin is evolved, and a subsequent fertilization brings full life to the ova, determining other features of the foetus. Thus, in the case of a pug bitch, which had a mongrel litter by a Skye terrior, and at her subsequent whelping by a pug dog, had some puppies with rough hair, these “influenced" puppies had the conformation of the pug all over, even to the twisted tail.

However, be the scientific part of the question what it may, the too common idea that a bitch having a mongrel litter will show influence of that litter in all future offspring, is utterly fallacious. Yours truly,

W. WADE. Oakmont, Pa., Sept. 14, 1896.

ENTOMOLOGY.

A New Character in the Colobognatha, with Drawings of Siphonotus.-In all known Diplopoda the external seminal apertures are located just behind the second pair of legs or in the coxæ of the second legs. In all Diplopoda except Polyxenus one or more pairs of legs are more or less modified to assist in copulation. In a great majority of forms the legs most modified are those of the seventh segment, but in two groups, the Omniscomorpha and Limacomorpha of Pocock the legs of the seventh segment are unmodified, while one or more pairs at the caudal extremity of the body are transformed into copulatory organs. The modification which has taken place in the Limacomorpha is very slight, for according to Mr. Pocock's descriptions and figures the last legs of Glomeridesmus marmoreus? consist of four or five joints and differ from the others mostly in being shortened and thickened. An equal or greater degree of specialization is now known to exist in other legs than those of the seventh segment, indeed, an almost equal peculiarity of structure is sometimes manifested by nearly all the male legs of certain genera of Polydesmida, Spirostreptida and Spirobolida. Especially noteworthy are the first pair of leys in Iulidæ, Parajulida and Pæromopodidae; the second pair of legs of Stemmatoiulidæ and Parajulidæ; the third pair in Striariidæ. Without detailing the very numerous and striking contrivances displayed by nearly all the anterior legs of some Craspedosomatidæ, it is sufficient to point out that in Scytonotus® modifications apparently as great as those of Glomeridesmus occur as far back as the twentieth pair of legs. In the light of these facts the degree of modification shown by Glomeri. desnius counts for little or nothing as an evidence of relationship with the Oniscomorpha. It might be said that Glomeridesmus has no copulatory legs at all, for the structures figured by Mr. Pocock are probably not comparable with the true copulatory legs of the other Diplopod groups, either in structure or function. The really remarkable thing about Glomeridesmus is that the legs of the seventh segment are not modified. Yet on this account we are not obliged to arrange Glomeridesmus in a separate category, for the degrees of modification to be found in the legs of the seventh segment of the other Diplopod groups are very various. It is even possible to trace, in the second pair of legs of the seventh segment of Craspedosomatidæ all the stages from the nearly normal to the completely modified condition. Thus with reference to the fact that the seventh legs are unmodified, Glomeridesmus may be looked upon as one end of a series, not necessarily farther removed from the other groups than they are from each other. Certainly the distance between the unmodified legs of Glomeridesmus and the distinctly jointed copulatory legs of Polydesmoidea and Polyzonoidea is not greater than that between those of the Polydesmoidea and the Spirostreptoidea.

| Edited by Clarence M. Weed, New Hampshire College, Durham, N. H. 2 Journ. Linn. Soc. Zool., XXIV, 475.

If, however, we admit that differences in the position and degree of modification of legs transformed for copulatory purposes are not of themselves characters of fundamental importance in the Diplopoda, we may seem to be under the necessity of admitting in addition that the constant appearance of what we may call the true copulatory legs in the place of the anterior or both pairs of the seventh segment is an evidence that the Helminthomorpha of Pocock are a homogeneous group to the extent of having more affinity with each other than with the Oniscomorpha. If, however, facts exist which indicate that the copulatory legs may have had independent origins in any of the Helminthomorpha the evidence just referred to is largely overthrown, for the utter diversity in plan of the copulatory legs of the different orders of Diplopoda is itself a strong indication that they represent independent lines of development. Such seems to be the import of the fact that the legs which in the Merocheta' are primarily transformed into copulatory organs, the anterior pair of the seventh segment, are in the Colobognatha entirely unmodified. Hence we must suppose that either the legs or the function have migrated, in case we assume a common origin and attempt to homologize the copulatory legs in the two orders. The theory of migration, however, has no facts to support it, and would be equally fatal to the idea that affinity or the want of it can in the Diplopoda be inferred from the position of the copulatory legs.

3 Am. N. Y. Acad. Sci., VIII, 233 (1894).

* An ordinal name to cover the Polydesmoidea, Craspedosomatoidea and Callipodoidea. Cf. Ann. N. Y. Acad. Sci., Vol. IX, (1895).

The fact that the Colobognatha have eight precopulatory legs is not new, but up to this time the whole eight have been supposed to belong to the first six segments. Both Latzel and Pocock give the distribution of these legs as in the second column. In reality the arrangement is that of the third column.

Latzel.

Siphonotus.
First segment,
First pair,

First pair.
Second segment,
Second pair,

Second pair.
Third segment,
Footless,

Third pair.
Fourth segment,
s Third pair,

Fourth pair.
( Fourth pair.
Fifth segment,
| Fifth pair,

Fifth pair.
Sixth pair.
Seventh pair,

Sixth pair.
Sixth segment,
Eighth pair,

Seventh pair.
First copulatory, Eighth pair.
Seventh segment,

Second copulatory, First copulatory.
Eleventh pair.

Second copulatory.
Eighth segment,
Twelfth pair,

Eleventh pair. My attention was first attracted to these facts while engaged in examining specimens of Siphonotus collected in Sierra Leone in December, 1893. The creatures were abundant in decaying banana stumps in Freetow, and I secured a large quantity. Instead of curling up as nearly all the representatives the present order are accustomed to do when placed in alcohol, my specimens remained conveniently straight and pliable so that they could be mounted in alcohol or balsam and studied to advantage. Of the arrangement of the legs as here stated there can be no doubt. The drawings are mostly camera tracings made from preparations in balsam. In order to make sure of the condition in Polyzonium, the genus studied by Latzel, I cut animals in two horizontally, brushed away the internal structures and mounted in balsam. Without such a preparation satisfactory observation is very difficult if not impossible in Polyzonium, for all the parts, especially the bases of the legs, are crowded together. I have examined in addition Andro, gnathus, Platydesmus, Pseudodesmus, Siphonorhinus and Siphonophorawithout finding any indications that the condition described is not present in all, though a final demonstration would in most cases not be easy without dissection.

5 Mr. Pocock seems to have come to doubt this disposition, for he uses a “?”in front of his last statement on the subject. —Max Weber's Reise, p. 335.

Prubably correlated with the comparatively slight degree of specialization which appears in the copulatory legs of the Colobognatha is the fact that in young males of Siphonotus the copulatory legs are severaljointed before maturity. Such a condition seems to be unknown in the other helminthomorphous groups.

In the previous discussion there bas been no intention to imply that the orders Oniscomorpha and Limacomorpha are not valid ; the conten. tion is merely that the position of the modified legs does not of iteli justify holding them as divisions of greater weight than other natural groups of Diplopoda, some of which have been designated by ordinal

It is to be expected that future study may result in a natural arrangement of the groups now designated as orders, but until their affivities are demonstrated nothing is to be gained by attempting to retain under one ordinal name and description animals which may prove to be widely divergent in their development history. Thus it is by no means impossible that the Colobognatha are really a group far. ther removed from the other Helminthomorpha than are some of these latter from the Oniscomorpha. Many of the peculiar characters of the Oniscomorpha are evidently the result of their power to roll themselves into a sphere, and are not to be assigned great weight in estimating affinities.

names.

Systematic Note. The genus Siphonotus bas not until very recently been reported since its establishment by Brandt in 1836. Within the last year or two Mr. Pocock has described species from St. Vincent (West Indies), Java and Celebes. To me it seems doubtful whether any of these species are congeneric with Brandt's type S. brasiliensis. Provisionally, however, the species of which drawings are presented may be described under Siphonotus, no doubt being possible that its affinities are here rather than with any other genus yet established.

Siphonotus africanus sp. n. Body slender, the sides parallel to near the ends, or very slightly converging cephalad.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][ocr errors][subsumed][subsumed][subsumed][subsumed][ocr errors][subsumed][subsumed][subsumed][subsumed][merged small][merged small][merged small][merged small]
« AnteriorContinuar »