436 DK S. F. HARMER AND DR W. G. RIDEWOOD ON THE 



pairs in the female and six pairs in the male. According to this observer (p. 8), 

 C. a?quatus is closely related to C. hodgsoni, but on p. 9 he says that it is nearly 

 allied to C. dodecalophus. 



At the first examination of the ccenoecium of the specimens obtained by the 

 Swedish Expedition it appeared to us that there was an even closer resemblance- 

 amounting, in fact, to a practical identity of characters between C. hodgsoni and 

 C. in&quatus. Since the latter is said to be characterised by a difference between the 

 two sexes in respect of the number of arms (female five pairs, male six pairs), it became 

 important to make a new examination of C. hodgsoni to ascertain whether any 

 difference could be detected between the two sexes in that form. Although the number 

 of male individuals examined was but small, the result of this inquiry was to confirm 

 the conclusion, suggested by the appearance of the ccenoecium, that C. inseqitatus 

 is a synonym of C. hodgsoni. It may be noted in passing that although the 

 memoirs containing the accounts of the two species in question were published 

 in the same year (1907), the name C. hodgsoni has the priority, as is shown by 

 the inclusion of the title of RIDEWOOD'S paper in the bibliography given by ANDKRSSON 

 on p. 115. 



In the original description of C. hodgsoni it is stated (RiDEWOOD, 07 1 , p. 55) that 

 " the normal number of plumes is twelve, but the sixth pair develop late, and a full- 

 sized polypide, with buds of its own, and with well-developed ovaries, may have only 

 ten fully-grown plumes." It is further remarked, however, that a vestigial sixth pair 

 can " usually " be detected in such cases, but that no individual has more than six pairs. 

 In his later paper (07 2 , p. 230) the same author states that " some polypides of 

 Cephalodiscus hodgsoni of full size and with mature gonads have five pairs of plumes 

 only." He does not discuss, in either place, the possibility that the difference to which 

 he alludes might be correlated with a difference in sex. 



We are in a position to confirm the substantial accuracy of ANDEESSON'S state- 

 ment with regard to the number of arms or plumes in the specimens described by 

 him as C. insequatus, though we think he has gone rather too far in asserting 

 (07, p. 6) that the number is invariable, in each sex, in the species examined by 

 him. The following is the result of an examination of 38 zooids in which the 

 arms were dissected from one another sufficiently to enable them to be counted 

 when the zooid was mounted on a slide. There is no doubt some element of 

 uncertainty in some of these estimations, particularly with regard to the presence or 

 absence of vestigial sixth arms ; but in the main the results can probably be accepted 

 as trustworthy. 



The material examined consisted principally of female zooids ; since, when the 

 gonads were sufficiently advanced in development to be recognisable as to their sex, 

 19 specimens were female and 3 were male. The remaining 16 specimens were 

 mostly advanced buds or quite young zooids in which the sex was not certainly 

 distinguishable. 



(ROY. soc. EDIN. TRANS., VOL. XLJX., 560.) 



