34 SUMMARY OF CURRENT RESEARCHES RELATING TO 



know the manner of incubation ;" and his belief led him to separate, 

 in his classification of Vertebrates, the Mouotrcmes from the Mammals. 

 Mr. Gill states other facts bearing on the subject. 



Embryonic Membranes of Marsupials.* — H. Caldwell finds, 

 from a study of Phascolarctns cinereus and Ilalmaturus ruJieolUs, that 

 " there is no vascular connection developed in any stages of develop- 

 ment between the embryo and the uterine wall." The attachment of 

 one to the other is effected by the cells of the subzonal membrane 

 beginning to enlarge and become amoeboid ; pscudopodia-like processes 

 are thrown out, which fit in between the cells of the uterine epithe- 

 lium, and serve to attach the blastodermic vesicle to the uterus ; the 

 attachment, however, is entirely non-vascular. The allantois has 

 an area of about 12 mm. in diameter, when best developed ; and, 

 though it becomes vascular in later stages, it never gives off' villi. 

 The arrangement in the Didclphia is so unique, that it throws little 

 light on the evolution of the placenta in the Monodelphia. 



Electromotive Function of the Fowl's Egg.f — L. Hermann and 

 A. V. Gendre find on applying electrodes to the developing egg of a 

 fowl that there is an electric current passing from the yolk to the 

 embryo ; the latter therefore is positive towards the yolk. The 

 current is so strong that it frequently suffices to drive the index off 

 the field of vision. The electromotive power may reach so high a 

 point as 1/100 Daniell. It appears to increase in strength in the 

 first stages of development, and reaches its maximum after about 

 eighty hours ; it then decreases. A similar condition has been 

 recently shown by Hermann and J. Mliller-Hettlingen in developing 

 plant embryos. 



Development of the Lesser Weever-Fish (Trachinus t?};era).J — 

 G. Brook describes the development of this fish. 



The egg, which is laid in the summer, is about 1 • 32 mm. in 

 diameter, and contains from twenty to thirty small oil-globules, thus 

 differing from the majority of floating fish-eggs hitherto described. 



In the unfertilized egg a vitelline membrane is easily distinguish- 

 able, but afterwards this comes in close contact with the zona radiata, 

 and often requires the action of reagents to show it proi^erly. 



The author's observations confirm those of Henneguy, that the 

 invagination observed in optic section in the living egg is an inward 

 folding of the lower layer of cells of the epiblast, and that afterwards 

 the alimentary tract is built up from this layer, together with material 

 derived from the intermediary layer. This point cannot, however, 

 be settled definitely without a careful examination of sections of this 

 stage. 



Ryder's observations are also confirmed as to the nature and 

 persistence of the segmentation-cavity, and in this respect pelagic 

 teleostean eggs seem to differ from all others hitherto described. 



Although the heart appears early on the fourth day, its venous 

 end remains closely applied to the vitellus up to several days after 



* Quart. Journ. Micr. Sci., xxiv. (1884) pp. 655-.58 (1 pi.). 

 t Pfliiger's Arch. f. gesammt. Physiol., xxxv. (1884) pp. 34-5. 

 i Journ. Linn. Soc. Lond. (Zool.) xviii. (1884) pp. 274-91 (4 pis.). 



