4'28 DR S. F. HARMER AND OR W. G. RIDKWOOD ON THE 



ends in close relation with the collar-canal (c.c.i.). The modus operandi of the collar- 

 canals has previously been discussed by both of us (HARMKR, 05, pp. 41-46 ; RIDEWOOD, 

 07, pp. 41-43). 



GILL-SLITS. 



The gill-slits (PI. II. figs. 5, 11, g.s.) agree closely with those of other species of 

 the genus. In the individual represented in figs. 6-1 1 , the external openings of the 

 gill-slits are seen from the plasticine reconstruction to lie in strongly marked 

 longitudinal grooves, each of which occurs nearer to the middle line of the anterior 

 wall of the metasome than the external opening of the corresponding collar- canal. 

 These grooves are, however, probably the result of contraction at the moment of 

 death. They can be traced along the metasome for a considerable distance, in an 

 aboral direction, beyond the collar-pores. The walls of the gill-slits are composed 

 of vacuolated epithelium (MASTERMAN'S " pleurochords "), as in other species of 

 Cephalodiscus. 



ALIMENTARY CANAL AND NOTOCHORD. 



The great length of the intestinal loop, which commences at the stomach and is 

 situated in the caecal end * of the metasome has been alluded to above in describing 

 the distinctive features of this species. It is well seen in the dissected specimen, 

 fig. 12, and in the sagittal section, fig. 16. In both figures the metasome is probably 

 shortened by muscular contraction ; and in its full state of extension the folds seen in 

 the figures would have probably disappeared. Owing to the length of this part of 

 the alimentary canal, the stomach (stom.) is separated by a considerable interval from 

 the caecal end of the metasome a character in which the present species resembles 

 C. levinseni. In one individual which has been examined, the intestinal loop contains 

 a number of Diatoms and other microscopic organisms, and many Sponge-spicules. 



The notochord (nch.) is seen in sagittal section in fig. 15 ; and as shown by this 

 figure, as well as by figs. 8-10, it has a well-developed lumen. 



GONADS. 



Every individual in which the gonads have been examined has proved to be of the 

 male sex. Although the amount of material at our disposal has been large, it was all 

 dredged at one time, and there is nothing to forbid the assumption that all the pieces 

 brought back by the Scotia were parts of a single large male colony. 



The testes vary a good deal in size in the different individuals examined. In their 

 highest development (figs. 5, 12) they are elongated organs, which may be simple 

 tubular structures, or may be marked by several constrictions extending traversely to 



* ANDERSKON (07, p. 7) lias pointed out, from observations on living zooids, that the " csecal end " of the metasome 

 disappears in fully extended zooids, where the stalk appears as a direct continuation of the body. The appearance 

 of a caecal end is none the less very characteristic of the majority of the contracted zooids. 



(BOY. soc. EDIN. TRANS., VOL. XLIX., 552.) 



