ON THE DEVELOPMENT OF THE ELASMOUKANCH PISHES, 355 



of the external gills, but later thau that I have not hitherto 

 succeeded in finding any trace of it. 



It was first seen by Gotte (loc. cit.) in the Batrachians, 

 and he gave a correct account of its development, and added 

 that it became the thoracic duct. 



I have not myself worked out the later stages in the de- 

 velopment of this body with sufficient care to be in a posi- 

 tion to judge of the correctness of Gotte's statements as to 

 its final fate. If it is true that it becomes the thoracic duct 

 it is very remarkable, and ought to throw some light upon 

 the homologies of the lymphatic system. 



Some time before the appearance of the external gills 

 another mass of cells becomes, I believe, constricted off" from 

 the part of the alimentary canal in the neighbourhood of the 

 anus, and forms a solid rod composed at first of dark 

 granular cells lying between the Wolffian ducts. I have 

 not followed out its development quite completely, but I 

 have very little doubt that it is really constricted off from a 

 portion of the alimentary canal chiefly in front of the point 

 where the anus appears, but also, I believe, from a small 

 portion behind this. 



Though the cells of which it is composed are at first 

 columnar and granular (fig. 12, s u, r), they soon begin to 

 become altered, and in the latter stage of its development 

 the body forms a conspicuous rounded mass of cells with clear 

 protoplasm, and each provided with a large nucleus. Later 

 still it becomes divided into a number of separate areas of 

 cells by septa of connective tissue, in which (the septa) capil- 

 laries are also present. Since I have not followed it to its 

 condition in the adult, I cannot make any definite statements 

 as to the fate of this body ; but I think that it possibly 

 becomes the so-called supra-renal organ, whicli in the Dog- 

 fish forms a yellowish elongated body lying between the two 

 kidneys. 



The development of the Wolffian Duct and Body and of the 

 Oviduct. 



The development of the Wolffian duct and the Oviduct in 

 the various classes of vertebrates is at present involved in 

 some obscurity, owing to the very different accounts given 

 by different observers. 



The manner of development of these parts in the Dog-fish 

 is different from anything that previous investigators have 

 met with in other classes, but I believe that it gives a clearer 

 insight into the true constitution of these parts than 

 vertebrate embryology has hitherto supplied, and at the same 



VOL. XIV. NEW SER. A A 



