~ 84 
we have to deal with an anterior extension of the mesone- 
phros, and conclusive proof of Calderwood’s hypothesis 
would only be 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, Weldont 
put forward the suggestion that they exist in the supra- 
renal bodies. But he thought that the latter bodies were 
very generally absent among Teleosts, whereas it is now 
known that they are present in all forms sufficiently in- 
vestigated. It is only the medullary portions which are 
present, however, and Grosglikt 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 
Kimery, this lymphatic tissue is to be derived from the 
peritoneal epithelium. It is a formative blastema which 
remains 7 statu quo on the reduction of the pronephros. 
D.—THE BLOOD VASCULAR 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 lamelle reaches a 
great loop-shaped vessel—the circulus cephalicus—lying 
beneath the base of the skull. From the circulus 
cephalicus, which contains oxygenated blood, the carotid 
arteries pass forwards to supply the brain and head, 
the cceliaco-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, 
t Loe. cit. { Anat, Anz., Jahrg., viii., pp. 605-611, 1885. 
