52 REPRODUCTION AND DEVELOPMENT OF TELEOSTEAN FISHES. 



my paper on Teleostean eggs and larvte published in the Transac- 

 tions of the Koyal Society of Edinburgh. Ryder described it in 

 the cod larva (Ann. Eep. Comm. of Fisheries of U.S. for 1882), 

 but gave what was a very natural but erroneous interpretation of it. 

 He called the space round the heart the pericardiac space, which is 

 true if taken etymologically but not morphologically. The venous 

 cavity he called the segmentation cavity, which is partially true, and 

 stated it was the same as the body-cavity, which is erroneous. 



Lastly, Mr. A. E. Shipley has described the development of the 

 heart in Petromyzon (Quart. Journ. Micros. Sc, Jan., 1887). His 

 description of the development of the heart from mesoblast beneath 

 the pharynx agrees with what I have described in Teleostei. He 

 also states that the heart communicates posteriorly with the space 

 beneath the ventral yolk-cells and the epidermis, and that such a 

 space would be equivalent to part of the segmentation cavity. Thus 

 the condition of things in Petromyzon is similar in these respects 

 to that in pelagic Teleostean ova. But when Mr. Shipley says, 

 " From the fact mentioned above that the mesoblast behind the 

 heart has not split into somatic and splanchnic layers nor united 

 ventrally, it will be seen that the cavity of the heart communicates 

 posteriorly with the space between the ventral yolk-cells and the 

 epidermis," I do not follow him. It seems to me to be a non 

 sequitur, — the heart might remain closed posteriorly until the ventral 

 mesoblast had developed in the region behind it. 



Moreover, although in Petromyzon it may be true that the meso- 

 blast behind the heart has not split into somatic and splanchnic 

 layers, my preparations show that the proposition is not true for 

 Teleostean larvae, for I find that the mesoblastic plates behind the 

 heart have split so as to form a coelom, and the splanchnic layer 

 forms a horizontal partition dorsally between the coelom on each 

 side and the blood space surrounding the yolk. And although it 

 may be true in Petromyzon that the yolk-cells form the immediate 

 boundary of the venous sinus internally, it is also possible that some 

 mesoblastic cells exist on the surface of the yolk in that form, for 

 Mr. Shipley has drawn his conclusions from the study of sections, 

 and I was not at first able to perceive in sections the dendritic 

 chromatophores I have described in the larva of the pelagic Teleostean 

 ovum. My observations concerning this subject have been chiefly 

 but not exclusively made on the ova and larvae of Pleuronectes 

 microcephalus. 



