CONTRIBUTION TO KNOWLEDGE OP EHABDOPLEURA. 631 



tine described by both Allman and Sars. The yellow cells 

 which line the stomach are ciliated (PI. XLI, fig. 8). I have 

 no special remarks to make with regard to the form or divisions 

 of the alimentary canal. It is is seen in the drawings of the 

 sections given in PL XLI, figs. 9 — 13. But in those sections 

 it will be observed that a space, though not a large one, inter- 

 venes between the body wall and the wall of the alimentary 

 canal (m). This is the body cavity or coelom, the existence 

 of which has been expressly denied by Prof. G. O. Sars. It 

 is easy to see the body cavity without having recourse to 

 the method of sections. Living specimens under slight com- 

 pression show it clearly enough on the oral face of the abdo- 

 men in the neighbourhood of the attachment of the stalk. It 

 can also be distinctly traced into the gymnocaulus or polypide 

 stalk (PL XL, fig. 12, B.C.). 



The tissue which bounds the body cavity consists of fusiform 

 cells tapering into fine fibres, sometimes branched. These cau 

 be detected both on the wall of the stomach and on the inner 

 face of the body wall, and occasionally they are seen stretching 

 from the stomach wall to the body wall. I have not been able 

 to detect any free floating corpuscles in the body cavity, nor 

 have I definitely traced it as a wide space into the lophophoral 

 arms and buccal-disc ; but it can hardly be doubted that in 

 the form of fine spaces between the deep tissues there is such 

 an extension of it. 



Skeleton. — One of the first facts of interest which I was able 

 to add to our knowledge of Rhabdopleura, as represented by the 

 memoirs of Allman and Sars, was the existence of a consistent 

 and extensively developed internal (mesoblastic) skeleton. This 

 consists of two chief parts, the skeleton of the lophophoral arms 

 (PL XL, fig. 1), and the skeleton of the contractile cord (PI. 

 XL, figs. 5, 11), or polypide-stalk, or gymnocaulus. The sub- 

 stance of which the skeleton is composed appears to be of a 

 cartilaginous consistence, and resists decomposition more 

 readily than the epidermic tissues, and can, consequently, be 

 readily demonstrated in a specimen which is commencing to 

 break up after death. 



