492 MR. G. W. BUTLER ON THE [JunC 14, 



Thus, considering the relations of the lung to the body-cavity, 

 we find that in the region anterior to the liver the cavity is reduced ; 

 and, tracing our sections baclcwards, we find that the anterior part 

 of the lung is surrounded on all sides by connective tissue. Theu 

 (still in the region of the heart) a small cavity appears on the outer 

 side of the lung, which {P^ in fig. 1'^), as we approach the apex of 

 the heart and the anterior border of the liver, extends round dorsad 

 of that organ. In sections that pass through the anterior apex 

 of the liver, the lung is bounded ventrally by a sort of incipient 

 fibrous-tissue " diaphragm," referable in part to a latero-anterior 

 ligament of the liver, and in part to a proliferation of connective 

 tissue that occurs on the ventral side of the lung, which we can 

 trace extending backwards over the ventral surface of its at present 

 free portion (* in fig. 2^). 



As remarked above, transverse sections taken anywhere else through 

 the liver show the lung projecting freely into the common pleuro- 

 peritoneal cavity, which wraps round it dorsally and ventrally, in 

 fact all round it, except on its left or mesial side where it is attached 

 (fig. 2^). When, however, we follow the sections still farther back, 

 behind the liver, we find that the posterior part of the lung burrows 

 as it were into the connective tissue dorsad of the body-cavity, a 

 little to the right of the aorta (fig. 3*). 



"We see, then, that at both ends there is a tendency to exclude the 

 lung from the general body-cavity, and at the same time to obliterate 

 the pleural cavity. Similarly, if, leaving the lung, we turn to the 

 left side of this embryo and follow the sections backwards, we find 

 that it is not till we reach about the middle of the liver that we see 

 the oesophagus projecting into the peritoneal cavity. For the 

 anterior part of its course it is for the most part surrounded by 

 connective tissue (figs, l'*^ and 2^). 



Again ; on the same left side of the body, just posterior to the left 

 lobe of the liver, we find a foreshadowing of the " posthepatic 

 septum," which later closes the liver-sacs posteriorly. This fore- 

 shadowing consists in a broadening and leftward extension over the 

 stomach of the m.edian ventral ligament. We note also that behind 

 the liver the body-cavity of either side is somewhat circumscribed 

 (fig. 3^). 



§ VI. (iii.). Embryo o/Elaphis quadrilineatus, 15 cm. long. 



My next stage is an Elaphis embryo 15 cm. long (Plate XXVIII. 

 fig. B). I regret not having a stage intermediate between this and the 

 preceding, or any embryo of another species of equivalent age. Still, 

 I think that a careful comparison of the 11 cm. and 15 cm. stages 

 leaves but little uncertainty as to how we ought to regard these peri- 

 toneal spaces of Snakes. 



Comparing the general features of the two embryos, we see that 

 the head has now a less embryonic appearance, the lower jaw, for 

 instance, being better developed. The umbilicus is further removed 

 from the cloaca, and sections show us that the gall-bladder and 



