ON THE ZOOLOGICAL STATION AT NAPLES. 453 
septum, that occurs in birds, crocodiles, and the Teiidee among lizards (ef. 
‘Proc. Zool. Soc.’ Nov. 19, 1889). In Tropidonotus the main abdominal 
cavity (which, if my description be correct, may contain nothing but the 
reproductive glands and their ducts, the intestine lying outside it) cannot 
be traced farther forward than the region where the gall-bladder, spleen, 
and pancreas are grouped together. ‘This is in the adult at a point some 
inches behind the posterior extremity of the liver, and corresponds 
approximately to the point where the reproductive viscera above referred 
to terminate anteriorly. Between the gall-bladder and the hinder end of 
the liver I see no trace of the body-cavity. Hach lateral half of the liver 
lies in aseparate closed sac, apparently corresponding to the ventral liver- 
sacs of birds. As to whether the body cavity has, in the region of the 
liver, any dorsal representative, Iam not prepared to speak. In Tropido- 
notws the somewhat sharp transition fromthe fleshy anterior part of the 
lung to the thin-walled sac that forms its posterior part, judging from the 
relation of the lung to the liver and to that part of the body cavity which 
surrounds it, seems to me to correspond to the transition from the lung 
proper to the air sacs of birds. 
The questions bearing on the structure of snakes that I would make out 
by the development are: What are the relations of the lung to the body- 
cavity? How does the constriction of the latter behind the liver come 
about? 
The preceding remarks may serve to remind the reader that the 
worker at the Zoological Station at Naples need not confine himself to the 
study of marine organisms. 
To turn now to the latter, and first to the question of the air-bladder. 
This is of course a wide subject, but the question that mainly interests 
me is this: Regarding the air-bladder of fishes simply as a diverticulum 
of the alimentary canal, what, if any, homologue has it in either the 
Hlasmobranchs or in the higher animals ?_ Even those who are satisfied 
with what is, I believe, the accepted view of the majority, that the ventral 
lung of the higher vertebrata and Dipnoi and the ventral air-bladder of 
Polypterus must in some way correspond to the dorsal air-bladder of the 
other Ganoids and Teleosteans, will admit that the developmental history 
of the air-bladder in the various types is at present vague, and that the 
origin, early history, and relation to each other of the various diverticula 
of the alimentary canal, considered as such, apart from their ultimate 
structure and function, are morphological questions of almost primary 
importance. 
As I understand the word it is impossible, by any straining ‘of its 
meaning, to say that a ventral outgrowth of the alimentary canal in one 
animal is homologous with a dorsal outgrowth in another, unless it can be 
shown either (1) that one is a later modification of the other, which now 
arises straight away by an abbreviation of development, or (2) that both 
are but different modifications of one and the same thing, such, for 
instance, as a pair of lateral outgrowths like the embryonic gill-pouchings. 
My work at Naples, as wellas general considerations, lead me to doubt 
whether any weight is to be attached to the ever-quoted lateral (Albrecht 
says it is only a little to one side of the mid-dorsal line) opening of the 
pneumatic duct in Hrythrinus. I find, for instance, in some of the Syn- 
gnathide that I have examined, where the embryo seems so stretched 
over a large mass of yolk as to make it easier for the alimentary canal to 
send out lateral rather than either dorsal or ventral outgrowths, that as a 
