248 DISCOVERY REPORTS 



The arms are situated on the dorsal side of the collar. Each arm is a hollow tubular 

 axis which may have an end-swelling (e.g. C. hodgsoni and C. kempi). The ectodermal 

 cells of the end-swelling are vacuolated and contain refractive beads. In C. nigrescens 

 and C.fumosus end-swellings are absent, but in C. detmis and C. sibogae, although there 

 are no end-swellings of the type described by Cole (1900, p. 256), refractive beads are 

 found the whole length of the dorsal side of the arms. Sections of C. densus stained in 

 Mallory show the vesicles and refractive beads very clearly (PI. XXXVI, fig. 2). Some 

 of the beads are stained blue and others red. They are ovoid or elliptical homogeneous 

 bodies and normally are in the middle of the vacuolated spaces of the ectodermal cells. 

 Some of these beads are sometimes found partly protruding from the surface of the cells. 



M'Intosh (1887, p. 11), who first observed the refractive beads in the end-swellings 

 of C. dodecalophus, described them as glandular. Masterman (1898 b, p. 344) suggested 

 that they were crystalline refractive lenses, and drew the inference that these organs are 

 rudimentary monostichous compound eyes similar in structure to the branchial organs 

 found in sedentary Annelids. Later he discarded this view, and Cole (1900, p. 356) 

 thought them rhabdite-producing organs. The greatest distribution of these refractive 

 beads occurs in C. densus and C. sibogae; in others they are restricted either to the 

 swollen tips of the arms or completely absent. The refractive beads therefore cannot 

 have any general function, but serve more or less a specific purpose which at present is 

 not understood. 



The arms grow from the dorsal wall of the collar on either side of the central nervous 

 system, and the collar coelom continues to the tip of each arm and into the pinnules on 

 each side; the whole system thus recalls the water-vascular system and tube feet of 

 Echinoderms. On the ventral side of the arm there is a longitudinal groove, termed the 

 food groove. The movements of the pinnules convey food particles into the groove along 

 which the particles move to the base of the arms. The food grooves of each side of the 

 body open into a space between the posterior lobe of the proboscis and the ridge on the 

 anterior margin of the collar. These together form an efficient tract for food particles 

 to the mouth. 



ORGANS OF THE TRUNK 



The greater part of the trunk is occupied by the alimentary canal. The pharynx is a 

 thick-walled chamber which in nearly all species extends half-way down the body and 

 opens by an obliquely directed narrow oesophagus into .the large stomach; this, on its 

 postero-ventral side, in turn leads into the intestine. The intestine is a narrow tube which 

 forms a loop and running upwards between the stomach and dorsal body wall opens into 

 a large rectum. The anus is on the dorsal side just below the collar, at the base of the 

 central nervous system. The gill slit on each side opens into the pharj'nx laterally at the 

 base of the post-oral lamella, below the collar pores. The wall of the gill slits is formed of 

 vacuolated cells. Transverse sections of the gill region show that the vacuolated cells in 

 the roof of the gill slit do not extend to the extreme front end of the pharynx as described 

 by Masterman (1898 b, p. 353), but that the floor of the gill slit continues backwards on 



