85 



The single pair of arms of the male C. sibogae agree in position with the first pair of 

 arms of an ordinary Cephalodiscus\ or, in other words, they are developed from the anterior 

 end of the dorsal side of the collar (figs. 72, 74). 



The metasome is much the largest part of the adult male, and it is almost entirely filled 

 by a pair of large testes, one of which is usually longer than the other. The body passes 

 gradually into a long, slender stalk, although I have not been successful in obtaining specimens 

 in which this is complete. It will be noticed that the stalk is attached to the extreme end of the 

 body, and does not originate from its anterior side as in the female zooids of other species. 



The young male (fig. 72) differs from an ordinary Cephalodiscus bud in no striking 

 character e.xcept that of the arms. The proboscis is of great size, as is usual in buds, and its 

 buccal disc overhangs the whole of the collar and metasome. The dorsal part of the collar 

 [c. 11. s.) is indicated by an obvious swelling, separated from the body by a constriction. From 

 the anterior region of this swelling originate the two characteristic arms, with their epidermis 

 crowded with refringent vesicles (not shewn in the figure). The left arm has been broken off in 

 this individual, but its torn base {L. a.) is clearly visible. The metasome is constituted by the 

 slightly swollen portion which immediately succeeds the collar, and it passes without any line 

 of demarcation into the stalk. 



Other young males, which differ in no essential respect from the above, are shewn in 

 fifaS. 73, 74. In some cases, indications of the alimentary canal, the collar-pores and the gonads 

 can be seen through the body-wall. In fig. 73 the right testis (/. r.) has reached a moderate 

 size, while the left testis, partially concealed by the right arm, is smaller. The left arm of this 

 individual is bifurcated at the tip. 



It will be noticed that the principal difference between the young and the adult male 

 is in the proportions of the metasome, which increases, concurrently wath the development of 

 the testes, to a large size, the other regions remaining stationary in their growth. 



A second adult male, in which the body-wall has been accidentally torn, is shewn in 

 PI. VII, fig. 76 and PI. IX, figs. 95, 96. The testes are elongated bodies which, as in several 

 other cases observed, shew constrictions or lobulations at intervals. The posterior end of the 

 left testis (/. /.) has been broken. The ventral lobe of the proboscis is turned dorsally, the 

 pigment-line being thus seen through its posterior epidermis. This position is favourable for 

 the examination of the mouth (fig. 95, w.), a more or less triangular aperture which appears 

 to lead into the vestigial alimentary canal indicated in the figures. Close to the anterior wall 

 of the pharyngeal portion of the alimentary canal are a pair of collar-canals {c. c). I have not 

 found gill-slits in any of the males, and in view of the absence of the tentacles, it is hardly to 

 be expected that they are present ; but the material is not sufficiently well preserved to enable 

 me to be certain of their absence. The rectal limb of the alimentary canal is indicated in 

 fig^- 95 1 96 by a slender cylindrical mass of cells (r.) which is seen near the left testis. 



The posterior view of the same individual (fig. 96) shews the distinct collar-swelling 

 indicating the position of the central nervous system {c. n. s.). Immediately posterior to this, 

 the metasome rises into a dorsal swelling, as in an ordinary female zooid; and on the anterior 

 part of this swelling, close behind the end of the collar, I believe that I have been able to 



