SUMMARY OF CURRENT RESEARCHES. 651 



sources he concludes that in the fertilised egg of all Metazoa the cen- 

 trioles of the first segmentation spindle are the direct descendants of the 

 centriole introduced by the spermatozoon. Contrary views are due to 

 too limited observations ; the time of appearance of the sperm centrum 

 is very variable and is apt to be missed, and the figure of the sperm 

 radiation may vary from the moment of origin to the time of complete 

 formation of the spindle. 



Impregnation and Fertilisation.* — E. Bataillon has made experi- 

 ments with the eggs of Pelodytes pundatus brought into contact with 

 spermatozoa of Rana, Bufo, and Triton. In one case the eggs of 

 Pelodytes were impregnated by spermatozoa of Triton alpestris, and 

 underwent irregular segmentation, the peculiarities of which are 

 described. The same spermatozoa had the same results on the ova of 

 Bufo calamita. In both cases the impregnation was followed by a 

 degeneration of the spermatozoon ; in the abnormal development the 

 stock of chromatin is derived from the female pronucleus. Impreg- 

 nation has a physiological role distinct from that of amphimixis. 



Trophoblast of the Placenta.f — Eternod finds that in Homo, many 

 Primates, and many other mammals, the ovum rapidly penetrates the 

 epithelium of the uterus, and encapsules itself in the mucosa, surround- 

 ing itself with a thick syncytial, epithelial envelope, formed from the 

 ectoderm. This trophoderm or trophoblast persists throughout the 

 whole period of gestation, and its history is briefly outlined. Chorionic 

 villi grow into the trophodermic epithelial mass ; the trophodermic 

 lacunas nearest the chorion dilate, and become reservoirs of maternal 

 blood ; the deep plasmodial layer of the trophoderm bordering the 

 chorion gives rise to two layers — one of distinct cells and one syncytial ; 

 the peripheral layer of the trophoderm continues to proliferate con- 

 tinuously, and gives rise to more or less extensive plasmodial or syncytial 

 prolongations ; one part of the superficial plasmodial layer adheres to 

 the uterine wall at the " Haft-Zotten." 



Absorption of the Yolk in Anguis fragilis.f — Ludwig Cohn finds 

 that in the slow-worm shortly before hatching, the residue of the yolk- 

 sac hangs in the body-cavity connected only with the mesenteric veins. 

 The assimilation of the yolk occurs in the epithelial cells of the folia of 

 the yolk-sac wall, which it enters in diffuse form, uniting again into 

 larger spherules. In structure and disposition the folia resemble those 

 of Lacerta. 



G-astrulation of Horned Toad.§ — Charles L. Edwards and Clarence 

 W. Hahn have studied embryos of Phrynosoma cornatum Harlan. It is 

 not viviparous, as usually stated, but lays its eggs (up to 25) in nests 

 formed in a chamber at the end of a tunnel which the female burrows. 

 The general process of gastrulation is similar to that in other reptiles, 

 but there are some striking differences. The egg stands in closer relation 

 to the lower Vertebrates than any other amniote, in that the protoplasmic 



* Comptes Rendus, cxlii. (1906) pp. 1351-3. 

 , t Arch. Sci. Phys. Nat., xxi. (1906) pp. 639-41. 

 $ Zool. Anzeig.fxxx. (1906) pp. 429 40 (6 figs.). 

 § Amer. Journ. Anat., v. (1906) pp. 331-51 (15 figs.). 



