360 SUMMARY OF CUKRENT RESEARCHES RELATING TO 



three weeks old; his results gain additional interest from the fact 

 that no embryo of this ago has ever been before examined. 



The branchial clefts, three in number, were of a very complex 

 form; the second, lying between the hyoidean and first branchial 

 arch, was entirely open ; the third descends in the form of a pouch on 

 the sides of the tracheal artery ; the origin of the thyroid gland is in 

 front of the base of the tongue ; the pancreas is represented by a 

 short coecum directed dorsally ; the presence of a commencing rudi- 

 ment of this organ is interesting from the fact that it has not been 

 discovered yet in larger embryos as long as 7 mm. ; the ureters open 

 on the ventral side of the cloaca, and not dorsally as has been erro- 

 neously stated ; two pairs of branchial arteries are present, the 

 hyoidean and the first branchial, as well as an unpaired artery, up to 

 the present unrecorded, which is given off from the aorta and accom- 

 panies the vitello-intestinal vessel ; the heart as yet only shows two 

 cavities ; the posterior extremity of the body presents the appearance 

 of a long tail, but it has no supernumerary vertebras, in fact, not 

 the full number, since the entire vertebral column only consists of 

 thirty-three vertebras. 



Placentoid Organ in the Embryo of Birds.* — M. Duval directs 

 attention to the sac which, in a chick, may be seen to be appended to 

 the lower end of the umbilical vesicle. Sections of smaller ova show 

 that both the outer and inner surfaces are formed by the chorion, and 

 that the inner surface developes villous processes which are plunged 

 into and absorb the mass of albumen ; they are supplied with vessels 

 from the allantois. Such an organ may, the author thinks, be well 

 called a placentoid sac. After having played its part as an organ for 

 the absorption of albumen, it undergoes atrophy. Duval thinks that 

 the discovery of this sac shows new points of affinity between pla- 

 cental and aplacental forms, and that its special structure in the bird 

 is due to the presence of a shell which forces the villi to be de- 

 veloped on the inner instead of on the outer surface of the chorion. 

 While the inner surface has a nutrient the outer has a respiratory 

 function, and therefore the sac is in all respects comparable to the 

 placenta of the Mammalia. 



Development of the Spinal Nerves of Tritons.f — M. Eedot finds 

 that, in Tritons, the spinal ganglion and the dorsal root of the nerve 

 are formed by a prolongation of cells which arises from the upper 

 part of the medullary tube and is never separated from it. The 

 ventral root is developed later, and at the expense of the medullary 

 tube ; it is (from at first ?) fibrillar in structure, and only becomes 

 secondarily united with the spinal nerve. The author remarks that, 

 although his conclusions differ from those of some very distinguished 

 observers, he does not despair of finding them confirmed. 



Poison of Batrachians.J— G. Calmels finds in the poison of the 

 toad a small quantity of methylcarbylamine, and describes the 



* Comptes Eendus, xcviii. (1884) pp. 447-9. 



t Arch. Sci. Phys. et Nat., xi. (18S4) pp. 117-46 (1 pi.). 



X Comptes Eendus, xcviii. (1884) pp. 5;-56-9. 



