A peculiar Stale of Development in Brachydesmus. 281 



XXXT. — A peculiar State <>f Development in Brachydesmus 

 {Myriapoda — Polydesmoidea). By Henry W. B&olehann 

 (of Pau, Basses -Pyrenees; France). 



My colleague, Richard S. Bagnall, of Penshaw, recently 

 accorded me the advantage of examining .some Myriapods 

 collected by himself, including ;i male representative of the 

 family Polydesniidae, which appeared to him to be of special 

 interest, and which was taken at Oxford in a mole's nest, 

 together with some other Polydesmids identified (by 

 Bagnall) as Brachydesmus superus, Ltz. (both sexes). 



The specimen here spoken of is undoubtedly referable to 

 the same genus, Brachydesmus, as shown by the shape of 

 the carinae, etc.; but, although probable, it is difficult to 

 decide as to whether it should be ascribed to LatzeFs species 

 or not, as it possesses only 18 body-segments, thus being at 

 the larval stage known as Pullus VI. 



To readers not familiar with the growth of Polydesmids, 

 it might be mentioned that the stage Pullus VI., which is 

 the one before the last for Polydesmids having .Mo body- 

 segments, is actually the last larval stage for those provided 

 only with 19, as in the case of Bracliydesmus. It is a well- 

 known fact that the sexually (and specifically) modified 

 8th pair of limbs of the male Polydesmids are far from 

 having acquired their normal form in the larva. Until the 

 last moult these organs are to be seen as two low semi- 

 cylindrical buds (fig. 1) pressed closely together and scarcely 

 protruding from the coxal opening located in front of the 

 9th pair of legs, which latter are normal ambulatory legs. 



When isolated and properly prepared, it is possible to 

 detect in these buds some darker, more thickly chitinized 

 regions still destitute of any definite outline ; such are at 

 least the only differentiations that have ever been mentioned 

 by authors acquainted with the subject. 



It was therefore greatly surprising to come across an 

 utterly different structure in the immature male Brachy- 

 desmus forming the subject of this note. Instead of the 

 low buds, a large membranous pouch-like body was found 

 to emerge from the coxal aperture (figs. 2 & 3). This 

 was considerably developed transversely, being apparently 

 composed of two pouches fused together. It was gibbous 

 anteriorly and slightly beut backwards so as to present 

 concave posterior surface, and situate on the apex we 



Ann. & May, N. Hist. Ser. 9. Vol. i. 19 



