DEVELOPMENT OF THE ELASMOBRANCH FISHES. 97 



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 position 

 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 de- 

 velopment 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) capillaries 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, which in the Dog-fish forms a yellowish elongated 

 body lying between the two kidneys. 



The development of the Wolffian Duct and Body and of tJie 



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. 



B. 7 



