Mr. A. Tulk on the Anatomy of Phalaiigium Opilio. 247 



mer 



ely leave an opening of communication at the anterior extre- 

 mity of the sacs. Between these two caeca is a groove or depres- 

 sion, which expands in front, and lodges the posterior division of 

 the trilocular heart, upon either side of which, resting partly upon 

 these crcca, is the upper pair of biliary vessels. Directly in front 

 of these large caeca are fom* rows of small ones, reaching as far 

 forwards as the anterior part of the thoracic cavity. The two an- 

 terior («'«', l)'b'), which lie against the sides of the middle optic 

 nerve, consist each of a pair of globular pouches ; the third row, 

 appearing to be formed of two upon either side {c'c'), has, in 

 reality, only one like the preceding, but divided by a deep con- 

 striction. The fourth and last row {d'd') seems also to be made 

 up of the same number, but the double character is here due to 

 the projection upwards of the rounded extremity of a pair of 

 caeca (ee), which open into the anterior end of two long inferior 

 sacs (PL IV. fig. 18. ee) presently to be described. Between the 

 four posterior pouches lies the middle chamber of the heart 

 (PI. IV. fig. 17. H), and upon them the loop of the upper biliary 

 tubes. The anterior division of the heart rests between the two 

 succeeding pairs. Inferiorly, but upon the sides of the alimentary 

 canal, is the pair of long caeca (PI. IV. fig. 18. C C) alluded to 

 above. Tliey arc longer and narrower, less flattened than the su- 

 perior pair, and widen out behind, u])on either side of the rectum 

 (r). Between them the gastric sac (G) forms a considerable dila- 

 tation dowaiwards. Upon either side of the intestine is a row of 

 four small flask-shaped sacs (PI. IV. fig. 17. a, b, c, d), bent down- 

 wards, when " in situ," against the sides of the abdominal cavity, 

 and which, commencing opposite to the anterior end of the large 

 superior caeca, diminish in size from before backwards, and reach 

 to their opposite extremity. Treviranus has described them as 

 opening into the two long inferior caeca, which is certainly incor- 

 rect. Tliey lie in the interval between them and the superior 

 pair, but are attached to another pair of elongated lateral eflec- 

 tions (B B) of the intestine, perfectly distinct from either of the 

 former, though partly concealed by them, and which have been 

 figured by llamdohrf under the title of the " grosse gefranztc 

 Seitenzotten," in allusion to theii- series of appended sacs. By 

 making a transverse section through the middle of the abdo- 

 minal viscera, as has been done at fig. 19, the relative posi- 

 tion of these (B B), and of the two other pairs of large caeca 

 (A A, C C), to the stomach is very well seen, as also the extent to 

 which they surround the ca\ity of the latter. It may be observed 

 likewise, that, owing to the pressure of these caeca, the upper two- 

 thirds of the gastric sac (S) presents an irregularly pentagonal 

 form, while below (*) its surface is convex. Upon the outer side 

 t Op. cif. 



