1893.] MR. A. E. SHIPLEY ON THE GESTXTS SIPTTNCDXtrS. 331 



canal, but into a well-developed system of lacunar spaces which 

 lies in the thick walls of the rectum. 



Section shows that the whole organ is hollow ; the walls of the 

 finer branches are one cell thick, and these cells seem to be shedding 

 their nuclei into the surrounding medium. The lumen of the 

 branches, and more especially of the main trunk, contains a gran- 

 ular coagulum in which numerous spherical granular corpuscles are 

 embedded ; these latter have very much the appearance of the 

 nuclei described above as being given off from the cells of the 

 branches, and it is quite possible that the latter are not all nuclei, 

 but some of them may be bodies elaborated in the lumen of the 

 organ and passing through the walls to the exterior, that is, into 

 the ccelomic fluid. 



The lacunar spaces into which these organs open are well 

 defined (Plate XXYII. fig. 10) ; they can be recognized without 

 the aid of sections, for if the rectum be cut out and examined 

 under a lens it becomes apparent that it consists of a thick inner 

 tube surrounded by a thinner, looser tube, which is supported by 

 four longitudinal mesenteries attached to the bodv-wall (Plate 

 XXYI. fig. 9). The space between the outer and inner tubes is 

 the space into which the rectal diverticula open, and its cavity 

 contains a coagulum similar to, and continuous with, that in the 

 cavity of the branching organ. The lacunar spaces do not extend 

 any great distance along the intestine, but are confined to a short 

 track about | an inch long ; they are split up by numerous 

 strands of connective tissue which run between the outer and inner 

 walls of the rectum. 



Until I came to investigate minutely the structure of the anal 

 tufts I had always regarded them as homologous with the anal 

 caeca of BonelUa, &c. Both their appearance and position seemed 

 to support this view. Closer study, however, shows that the 

 structures in Sipuneulus differ very considerably from those in 

 BonelUa. In the first place, they do not open into the coelom : the 

 ciliated funnels at the end of the branches in the anal c£eca of 

 armed Gephyrea are well known, nothing of the sort is found in 

 Sipuneulus. Secondly, they do not open into the lumen of the 

 intestine but into a well-developed system of lacunar spaces in 

 the wall of the rectum. These differences seem to throw much 

 doubt on the view that any homology exists between these struc- 

 tures in the two groups. 



If we may make any inference from the structure of the gland 

 to its function, it appears probable that this branching gland has 

 somewhat the same functions as the lymphatics and the numerous 

 glands which in all classes of animals exercise some influence on 

 the constituenta of the circulating medium. 



List of Papers referred to. 



(1) Kefeesteix, W. — '■' Beitriige zur anatomischen und systera- 

 atischen Kenntniss der SipuncuHden." Zeitschr. f. wiss. 

 Zool. Bd. xy. 



