4 W. G. RIDEWOOD. 



The range iu the uumljer of pinnules of the plumes in the same species, and even in 

 difterent plumes of the same individual, is too wide to allow of such character being 

 utilised for purposes of discrimination. Although the two plumes of the males of 

 C. sihogae have no pinnules, those of the neuter individuals are provided with pinnules 

 resembling those of other species. The massiveness of the axes of the plumes of 

 C. nigrescens is distinctive of that species, but as regards the form of the apex it is not 

 easy to say whether in C. nigrescens the apex is swollen or not, it varies so much with 

 the different degrees of extension and contraction of the plumes {cf. figs. 23 and 24, 

 plate 5). Terminal bulbs with refractive colourless beads such as occur in C. dodeca- 

 lophus (text-fig. 1) are met with in C. hodgsoni (figs. 31 and 32, plate 5), but there are 

 no such swellings in the polypides of C. levinseni, in the neuter polypides of C. sibogae, 

 nor in the adults of C. gracilis, although in the buds of the last species they occur on 

 the first and sometimes on the second and thii-d plumes, and occasionally persist in the 

 adult stage (10, p. 20). In males of C. sibogae the refractive beads occur along the 

 whole course of the two pinnule-less plumes. 



^•^■%' 



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Text-Figube 1. — Ceplialodiscus dodecalophus ; plumes seen from the aponeural aspect and from the side. 



The size of the body of the polypide varies somewhat with the condition of the 

 gonads, but it is fairly uniform for the same species, and would be a useful character if 

 one could estimate the bulk or the weight of the body. In consequence, however, of 

 the great mobility of the parts, and their capacity for expansion and contraction, the 

 linear measurements arc not very reliable, and the length of the body of C. levinseni 

 and C. nigrescens may be an excessive index of the bulk of the body in consequence of 

 the limitation imposed upon the width of the body by the narrowness of the tubular 

 cavity in which the polypide dwells. C. dodecalophus and C. /lodgsoni, on the other 

 hand, being less restricted, have a body less cylindrical. 



The measurements found to be most reliable are those from the front of the buccal 

 shield to the posterior end of the visceral mass. The length of the body of C. dodeca- 

 lophus is usually given as 1 mm., but it is not explained how this measurement is 

 taken ; presumably one is expected to measure from the anus to the end of the visceral 

 mass, but even then the recorded measurement falls short of the actual size. The 

 average length of the polypide from the front of the buccal shield to the end of the 



