46 
MONICA TAYLOR. 
they are covered by the operculmn. When branchial respira- 
tion is just beginning the gill-chamber opening is a single 
crescent-shaped one; as development proceeds the arms of 
the crescent are gradually obliterated, owing to the fusion 
of the backwardly growing operculum with the body-wall, 
and a single median ventral opening is the result. 
(6) There is a blind diverticulum in the dorsal roof of the 
mouth behind the hyoid. 
(b) Alimentary Canal. 
(!) The alimentary canal has a typical Teleostean character 
and development, is solid at first, hollowed out secondarily, 
and has no obvious connection with the yolk. 
(2) No air-bladder has been detected at any stage. 
(3) The pyloric valve arises by outpushings of the 
intestine. These blind cmcal outgrowths have the appear- 
ance of very short rudimentary pyloric cieca. 
(4) Apart from these structures there are no pyloric caecn. 
(5) The pancreas is an elongated compact gland arising 
from a dorsal and two ventral rudiments. 
(6) The liver is elongated and unilobed. 
(7) There is a typical thymus arising from clefts 2, 3, 4 and 5. 
(8) A thyroid arises as a solid median derivative of the 
floor of the pharynx. It is elongated and bilobed anteriorly. 
(9) The spleeu develops early, is very conspicuous, and 
multilobed at first. 
(c) Renal Organs. 
(1) The pronephric chamber and tubule are formed from 
the nephrotome of the third trunk myotome. 
(2) There is no communication at any time between 
splanchnocoele and nephrocoele of the pronephros. 
(3) The archinephric duct is formed from the nephrotomes 
of the segments posterior to the third; the conversion of these 
nephrotomes into a duct takes place simultaneously, involv- 
ing no backward growth of the archinephric duct. 
