52 A. Alcock— On the Gestation of Blasmohranch Fishes. [No. 1, 



is formed. The maternal attachment of each placental cord is separate 

 and distinct. 



At the foetal end, the cord, having pierced the ventral wall between 

 the pectoral fins of the foetus, divides into two branches. The lower of 

 these, which is the artery, can be traced into the mesentery, where, 

 at the level of the proximal end of the large intestine, it is found to 

 be furnished, with a pouch-like gland : its connexion with the dorsal 

 aorta could not be made out. The upper branch (venous) subdivides 

 into two branches, which ascend in the median fissure of the liver to the 

 portal vein. 



A transverse section of the placental cord shews one artery and one 

 vein. 



A transverse section through the wall of the uterus shows an outer, 

 thin, compact layer of muscular and connective tissue; but the greater 

 part of the section consists of an indefinite spongy network (venous ?), 

 with numerous large thick-walled arteries. 



The red blood cells of the foetus are y^Vo 0I an inch long, and 2 3 * 9 

 of an inch broad. 



b. Zygakna blochii. On the same occasion, a female of this 

 species, nearly five feet long, was taken. The general appearances were 

 similar to the appearances in Carcharias melanopterus ; but each uterus 

 contained five foetuses ; and the placental cords, which were much more 

 delicate, were uniformly covered, except at the extreme foetal end, with 

 flattened, leaf-like, bilobed or trilobed appendicula, from one-eighth 

 to one-quarter of an inch long, each lobe being about one-eighth of an 

 inch broad. 



A transverse section of a placental cord, which includes vertical 

 sections of the peripheral appendicula, shows, in the cord, a single 

 artery a large vein, and four large irregular channels ; and, in each 

 of the appendicula, a central longitudinal vessel apparently opening 

 into one of the channels of the cord. 



A single intact appendiculum, examined under a moderate power, 

 is seen to have a thick external epithelial investment, while internally 

 the central vessel is seen to break up into a fine ramifying and anasto- 

 mosing capillary-like plexus. 



A transverse section of an appendiculum, under a high power, 

 resolves the epithelium-like investment into a gland-like aggregation of 

 round laro-e-nucleated cells, about ten strata deep, beneath which is the 

 loose-meshed connective tissue of the appendiculum which supports 

 the ramifying branches of the contained vessel. 



The structure of the placenta, and the ultimate distribution of the 

 vessels of the cord, are the same as in Carcharias melanopterus, but there 



