1892.] BODY-CAVITY IN SNAKES. 489 



§ V. Explanation of the List of Snakes given in § III. 



a — sigirities a Snake in which I have clearly found the full com- 

 plement of peritoneal spaces as described above, § IV., viz. : — 

 a. The posterior peritoneal space. 

 /3. The paired liver-sacs, 

 y. The gastric sac of left side. 

 d. The " omental " space. 

 h — signifies a Snake in vrhich I have not clearly made out the 

 " omental " space, though all the others occur ; 



but * indicates that this probably is present. 

 „ J „ „ possibly „ 



c — signifies a Snake in vphich I have not clearly made out either of 

 the smaller peritoneal spaces, i. e. either the " gastric " or the 

 " omental," though the principal sacs, viz. the two liver-sacs and 

 the posterior peritoneal space, occur. 



t indicates that a Snake probably has a " gastric " sac. 

 tt „ ., „ possibly ,, „ ,, 



I — Typhlops. — In this the anterior and posterior boundaries of the gastric 

 sac were not clearly made out. 



z—DryopMs (one of the long " Whip Snakes "). — I cannot pretend to have 

 seen the posterior boundary of tbe liver-sacs, but have no reason to 

 believe that they are not closed as in all other cases. 



3 — Lamprophis. — It is possible that the right testis is enclosed in a separate 

 peritoneal sac apart from the posterior peritoneal space. If so, this 

 would be a peculiarity of this Snake. 



4 — Vipera nasicornis. — I am not sure that the gastric sac does not com- 

 municate with the posterior peritoneal space. If it does, we merely 

 have a persistence of a condition of things which (see § VI.) certainly 

 does persist to a comparatively late embryonic stage. 



The list in § III. in part speaks for itself. I may point out, 

 however, that Snakes marked b and c are essentially similar as to the 

 relations of their peritoneum to those marked a. The "gastric" 

 and still more the " omental " space is as a rule small, and anyone 

 who did not know exactly where to look for either would in most 

 cases not find them. Where there was no clear indication of one or 

 both, I have marked the Snakes & or c as explained ; and it is quite 

 possible that one or both of them may be found in Snakes so marked. 

 Moreover, even if they are absent this does not indicate any hard- 

 and-fast dissimilarity between the Snakes marked b and c and those 

 marked a, for development (§ VI.) shows that both the " gastric " 

 and the " omental " spaces are, with rare exceptions, but reduced 

 remnants of original more extensive ones ; and a comparative 

 study of the Snakes on the list shows that when these spaces are 

 present, the amount of reduction of either varies very greatly, not 

 only in different species but in different individuals of the same 

 species. It is not then surprising, but, rather, just what we 

 should expect, that in some cases one or both of these spaces should 

 have become obliterated altogether. 



