ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 29 



uterine mucous membrane during gestation and the constitution of the 

 placenta. The conclusions are briefly as follows : — (1) The uterine 

 mucous membrane thickens, forms papillae covered with epithelium and 

 separated by crypts and glands. (2) Neither glands nor uterine 

 epithelium share in formation of the placenta. The ends of the glands 

 persist throughout gestation, papillae and epithelium degenerate. 

 (3) The vessels of the mucous membrane become surrounded by 

 increasing sheaths of cellular elements. (4) The endothelium of such 

 vessels degenerates, the nuclei break up, and chromatic granules fill the 

 cavity of the vessels. (5) Leucocytes at first present in the mucous 

 membrane, pass through certain changes in the middle stages, and are 

 lost. (6) Before the attachment of the embryo, two layers in the 

 embryonic ectoderm are distinguishable — a deeper of cylindrical cells, 

 a superficial of irregular elements and clusters of nuclei. To the basis 

 afforded by the uterine mucous membrane this superficial layer becomes 

 united. It then developes enormously and forms a multinuclear mass 

 into which the deeper layer sends processes including ectoderm and 

 somatopleure. 



The maternal capillaries enter this multinuclear layer of foetal 

 origin, lose their endothelium, and are continued into a system of 

 numerous lacunae without definite walls. The allautois forms a richly 

 vascular connecting axis, round which allantoic villi are formed. The 

 maternal blood in the lacunae is separated from the vascular villi only by 

 the multinucleated protoplasmic layer. 



The rabbit's placenta is thus of foetal origin formed by allantoic 

 villi ramifying in a tissue derived as above described. In the same 

 tissue the vessels of the uterine mucous membrane, formed into a 

 system of lacunae, are also included. A complete memoir, with figures 

 and details, is forthcoming. 



Neurenteric Canal in the Rabbit.*— Prof. C. Giacomini has investi- 

 gated the neurenteric and the anal canals in the embryo of the rabbit. 



(1) At two different epochs, there are two connections between the ecto- 

 dermic and endodermic surfaces — viz. the neurenteric and the anal canals. 



(2) These communications are ephemeral, and speedily disappear in 

 consequence of the modifications at the two extremities of the primitive 

 line. (3) They are intimately associated with the development of the 

 primitive line, or rather of the primitive groove. Hardly has the 

 primitive line become apparent and begnn to extend backwards, than 

 the anterior connection or neurenteric canal becomes patent. When the 

 primitive line has attained its maximum development in length, the 

 posterior connection or anal canal developes. These connections are 

 both produced by a bending inwards of the ectoderm to meet the 

 endoderm. The anterior invagination precedes and evokes the meso- 

 derm ; the posterior invagination is formed when the mesoderm has 

 already been developed between the primary layers. The former is 

 therefore primary and essential, the latter secondary or dependent upon 

 the special conditions of development. Prof. Giacomini inclines to the 

 hypothesis that the two communications at the ends of the primitive line 

 and groove are together homologous to the single blastopore, and that in 

 the ideal ancestral vertebrate medullary canal and gut bad a common 

 external aperture, the blasto-neuro-pore. 



* Arch. Ital. Biol., x. (1888) pp. 273-94 (1 pi). 



