84 



we have to deal with, an anterior extension of the mesone- 

 phros, and conclusive proof of Calderwood's hypothesis 

 would only he afforded by tracing the embryonic 

 pronephros into the structure so termed in the adult. 



Concerning the representative of the lymphatic head 

 kidney of Teleostean fishes in higher vertebrata, Weldonf 

 put forward the suggestion that they exist in the supra- 

 renal bodies, l^ut he thought that the latter bodies were 

 very generally absent among Teleosts, whereas it is now 

 known that they are present in all forms sufficienth' in- 

 vestigated. It is only the medullary portions which are 

 present, however, and GrosglikJ has suggested that the 

 homologues of the cortical parts of the suprarenal bodies 

 of higher vertebrata are present in Teleosts as the 

 lymphatic portions of the head kidney. According to 

 l*]mery, this lymphatic tissue is to be derived from the 

 peritoneal epithelium. It is a formative blastema which 

 remains in statu quo on the reduction of the pronephros. 



D.— THE BLOOD VASCULAE SYSTEM. 



The heart in Pleuronectes, as in all fishes, is a respira- 

 tory one, and consists of a single auricle and ventricle. 

 The de-oxygenated blood which it contains is propelled 

 into the gills, and after passing through the respiratory 

 capillary network in the branchial lamellae reaches a 

 great loop-shaped vessel — the circulus cephalicus — lying 

 beneath the base of the skiill. From the circulus 

 cephaliciis, which contains oxygenated blood, the carotid 

 arteries pass forwards to supply the brain and head, 

 the coeliaco-mesenteric artery enters the body cavity 

 and supplies the viscera, while the rest of the body 

 is supplied by the dorsal aorta. De-oxygenated blood, 



\ Loc. cit. \ Anat. Anz., Jahrg., viii., pp. 605-611, 1885. 



