442 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Spermatogenesis in Batrachoseps.* — Dr. G. Eisen publishes a pre- 

 liminary account of the spermatogenesis in B. attenuates. The testes 

 contain four distinct kinds of cell — polymorphous spermatogonia, 

 auxocytes, spermatocytes, and spermatids, which originate from one 

 another in the order mentioned. There are, after the polymorphous 

 spermatogonia, four generations of round cell spermatogonia, then auxo- 

 cytes, &c. He describes the various constil uents of the cells and uses 

 a somewhat complex nomenclature. Even if we restrict attention to 

 the fibres, we are confronted with mantle fibres, polar fibres, central 

 spindle fibres, contractile fibres, retractile fibres, and fibre cones. In 

 the mitoses, a radiosomic and a chromosomic process are sharply distin- 

 guished. The cytosome proper contains no permanent structures of any 

 kind. The plasmosphere, hyalosphere, granosphere, the various kinds 

 of fibres, as well as the central spindle, are all ephemeral structures 

 which are developed by re-arrangement of pre-existing granula, and 

 which again disperse when their function is over. The granula are of 

 at least four different kinds, and one kind is never converted into any 

 other. 



Dental Ridges in Birds.'! - — Dr. H. D. Tjeenk Willink finds that in 

 Gallinula chloropus, Sterna hirundo, St. cantiaca, Hsematopus ostralegus, 

 CEdicnemus crepitans, and Numenius, there are, in the mouth-cavity, be- 

 sides many other ridges and thickenings, two lateral ridges, the so- 

 called dental ridges. In Numenius they are seen only for a short period 

 of embryonic life; in Limosa segocephala they are altogether absent. The 

 ridges do not appear to have any embryonic function. In Numenius, 

 especially, they are vestigial structures. They occur in the position of 

 dental ridges, and each arises as a thickening of the epidermis, which first 

 projects from the epidermis, and later on sinks deeply into the mesoderm. 

 They are certainly vestigial dental ridges. The author also discusses 

 the other ridges, e.g. the lip-ridges and the egg-tooth. 



Experimental Embryology.; — E. Bataillon has experimented with 

 the eggs of the lamprey (Petromyzon planeri), subjecting them to isotonic 

 saline and sugar solutions. The segmentation is much changed in 

 response to the altered conditions of osmotic pressure. The results seem 

 independent of the chemical nature of the solutions. 



The third plane of cleavage, which is normally horizontal, is always 

 vertical in the solutions. The early segmentations tend to be unequal, 

 recalling those in Nassa and some other Molluscs. The altered rate of 

 development (delayed), the irregularities of cleavage, the point of arrest, 

 seem all to depend on the osmotic pressure. Some experiments on com- 

 pression between vertical plates are also reported. 



Experimental Polyembryony. § — E. Bataillon has observed the 

 results of transferring fertilised ova of Petromyzon planeri to solutions 

 of sugar (10 per cent) or of salt (1 per cent,) for eighteen hours, and 

 then returning them to ordinary water. The changes in the egg's 

 osmotic pressure thus induced bring about a separation of blastomeres ; 

 the first two or three proceed to develop in isolation. Thus he observed in 



* Biol. Bulletin, i., No. 2, 1900, pp. 99-113 (16 figs.). 



t Tydschr. Nederland Dierk. Ver., vi. (1899) pp. 243-54 ( 1 pi.). 



t Comptes Rendus, cxxx. (1900) pp. 1413-5. § Tom. cit, pp. 1480-2. 



