802 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



He adduces experiments to controvert Eombout's view that a fly can 

 maintain itself on a glass surface by one leg only if that surface be 

 vertical and if the body of the fly be in contact with the glass. 



7. Prototracheata. 



Development of Peripatus capensis.* — Mr. A. Sedgwick has 

 found that the embryos of Peripatus capensis remain thirteen months 

 in utero, and young ova pass into the uterus a month before last year's 

 young are born. Fertilization seems to be effected in the ovary, and 

 segmentation and the early stages of development take place in the 

 oviduct ; the ripe ovum is elliptical in shape, and is rendered opaque 

 by the granules of food-yolk. Segmentation is complete, and at its 

 end the ovum consists of a number of large endoderm cells scattered 

 irregularly within the egg-membrane, while the ectoderm cells form 

 a mosaic which is closely applied to the membrane on one side. 

 After the endoderm cells have grown together, the ectoderm rests on 

 them like a cap, then grows around and completely incloses them 

 except at one point, which is the blastopore. A cavity next appears 

 in the centre of the endoderm cells, and the blastopore elongates ; at 

 its hinder end there is an opacity — the primitive streak. The meso- 

 derm arises from the proliferation of the undifferentiated cells of the 

 streak, and grows forwards in the form of two ventro-lateral bands ; 

 these divide transversely from before backwards into somites ; the 

 blastopore begins to divide into mouth and anus, and the primitive 

 streak becomes marked by the primitive groove. 



The ectoderm, except where it gives rise to the nervous system, is 

 always unilaminate ; the entire central nervous system developes from 

 continuous ventrolateral thickenings of the ectoderm. In front of 

 the mouth they are enormously developed, but they never separate 

 from the ectoderm to which they owe their origin, as the latter is 

 invaginated in the form of two longitudinal furrows, which become 

 deeper and close in exactly the same way as the medullary groove of 

 a vertebrate embryo. The two closed vesicles thus formed become the 

 cerebral ganglia. 



The body-cavity is very complicated and divided into several 

 parts ; the cavities in the legs are derived from those of the somites ; 

 where the former communicate with the exterior they give rise to the 

 segmental organs, which, therefore, in Peripatus, as in Elasmobranchs, 

 are direct modifications of parts of the primitive body-cavity. 



In a later communication^ Mr. Sedgwick enters into further details. 

 He finds that the " testes " of Balfour are seminal vesicles, and the 

 true testes the so-called " prostates." The ovary is really paired and 

 consists of two tubes closely applied together ; the ova are derivates 

 of the epithelial lining of these tubes ; the ovaries always contain 

 spermatozoa ; the male deposits little oval spermatophores quite 

 casually on any part of the body of the female, for example, they 

 have been observed on the head. But it is quite unknown how they 

 make their way into the ovaries. 



* Proc. Roy. Soc, xxxviii. (1885) pp. 354-61. 



t Quart. Journ. Micr. Sci., xxv. (1885) pp. 449-56 (2 pis.). 



