306 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the primary bilateral rudiment become actual sex-cells ; the rest degene- 

 rate at ontogenetic stages varying according to the species. A second 

 lineage of gonocytes arises by modification of the germinative cells due 

 to the proliferation of the peritoneal epithelium. These invest the 

 surface of the reproductive organs and form a germinative epithelium. 

 The number of gonocytes is subject to considerable fluctuations. The 

 gonocytes of both first and second lineage may become capable of fer- 

 tilisation. They never fuse together, and never become follicular cells. 

 If from any cause sexual development is arrested, these cells undergo 

 degeneration. 



The last part of the paper discusses the bearing of these results on 

 the general theory of the evolution of genital organs. The author con- 

 siders that they bring the organogenesis of the reproductive organs 

 entirely into line with what is known in regard to other Vertebrates, 

 differing in this opinion from Bouin, whose investigations on Rana led 

 him to regard Weismann's theory as inapplicable, and even to deny that 

 there is any cellular specificity. 



Origin of Germ-cells in Mammalian Embryos.* — W. Paibaschkin 

 finds that in the rabbit on the thirteenth day the ccelomic epithelium of 

 the median part of the Wolffian body attains the character of a germinal 

 epithelium. At this stage there are found also single germ-cells outside 

 the germinal ridge, lying mainly under the aorta in the mesenchyme 

 tissue. On the eleventh day the germinal epithelium (in the old sense) 

 is not formed, only single germ-cells are to be found in the epithelium of 

 the median part of the "Wolffian body. On the tenth day no germ-cells 

 are to be found here, although single germ-cells are found in the dorsal 

 parts of the mesentery, and in larger numbers in the ventral mesentery 

 and surrounding the hind gut. These last exhibit amoeboid movement. 

 The youngest stage at which germ-cells were traced was in ninth-day 

 embryos, in which they lie close to the epithelium on the hind gut and 

 mainly in its ventral section. Thus it appears that the place of origin 

 of the germ-cells lies at some distauce from the germ-gland region, and 

 that the germ-cells occur much earlier than has hitherto been assumed. 



&* 



Development of the Frog's Head.f — Agnes I. M. Elliot deals with 

 the development of the segments of the occipital region of the skull. 

 In front of the myotome associated with the first spinal nerve and its 

 ganglion there are in the 9 mm. tadpole two myotomes. Cartilaginous 

 arches appear in connection with these and fuse with the parachordals 

 from which they are still distinct in a 20 mm. tadpole. Both these 

 myotomes and a rudimentary ganglion associated with one of them 

 disappear, while the cartilaginous arches corresponding to them form 

 the occipital region of the skull. The vagus arises by numerous roots. 

 It is suggested that the hinder roots may represent ventral roots of 

 the nerves of the missing post-otic segments and also of the segment in 

 which the first myotome is developed. The segmentation of the post- 

 otic region of the skull agrees in Rana with that in Necturus. 



* Anat. Anzeig., xxxii. (1908) pp. 222-4. 



t Quart. Jouru. Micr. Sci., li. (1907) pp. 647-57 (2 pis.). 



