REPORT ON THE CRINOIDEA. 103 



and therefore presents tlie usual reticular structure after the limestone has been removed ; 

 and even those bands of ordinary connective tissue (both in Comatula3 and in Pentacrinus) 

 which contain irregular limestone deposits have a totally different facies from the blood- 

 vessels (PI. LVII. fig. 5). They meet at different angles, and have no internal cavity 

 which is lined by epithelium and frequently contains coagulum. 



The relation of the plexiform gland to the intervisceral blood-vessels is especially well 

 seen in Actinometra. 



Owing to the excentric position of the mouth, the characters of the plexiform gland are 

 considerably different from those of the same organ in the regular Crinoids. I have 

 studied it more particularly in the two species Actinometra j^arvicirra and Actinometra 

 'pulchella, the latter having the mouth much nearer to the centre of the disk than the 

 former. It is also radial in position, while that of Actinometra parvicirra is interradial. 

 In both types the labial plexus is most developed behind the mouth, and especially 

 towards the left or eastern angle, where it contains an imperfectly differentiated spongy 

 orsan ; and it also extends outwards between the ambulacra farther than on the 

 right side. 



It is the right anterior portion of the labial plexus, however, which is more especially 

 connected with the plexiform gland, while the spongy organ at the left posterior angle of 

 the mouth passes backwards into the intervisceral vessels. 



In Actinometra pulchella with its radial, and but slightly excentric mouth (PL LXI. 

 fig. 1), the relations of the parts are, as might be expected, much more like those of Antedon 

 than is the case in Actinometra jMrvicirra, with its nearly marginal and interradial mouth 

 (PI. LXI. fig. 2). In the former type the plexiform gland rising out of the calyx ascends 

 nearly in the vertical axis of the disk for some little distance and then divides into two 

 principal portions. The left hand one is little more than a bundle of vessels which runs 

 forwards, upwards, and a little outwards till it comes to lie above the gullet imme- 

 diately in front of the base of the anal tube, and terminates in the spongy part of the 

 labial plexus at the left posterior angle of the mouth. The right division, which is connected 

 with the intervisceral vessels of the anterior half of the disk, retains its glandular character, 

 and passes upwards between the coiled gut and the central rectum to join that part of 

 the labial plexus which lies beneath the origins of the ambulacra of the right side. 



The fore-gut of Actinometra parvicirra passes more directly backwards and down- 

 wards than that of Actinometra p>ulchella, until it comes to lie immediately above 

 the base of the posterior ray, rather to the left of the centre of the disk (I'l. LXI. fig. 2). 

 The spongy organ at the left posterior angle of the mouth is continued downwards and 

 backwards slightly above the gullet, between it and the three inner coils of the gut, as a 

 gradually diminishing bundle of vessels, with which the intervisceral vessels of the left half 

 of the disk are connected. This corresponds to the left division of the plexiform gland in 

 Actinometra pulchella, though not quite in the same position as regards the digestive 



