xlvi THE VOYAGE OF H.M.S. CHALLENGER. 



assume from the similar character of the petasma in the male Lucifer, and in the 

 Penseidse, that the means adapted for impregnating the female in Lucifer is also that in 

 the Penseidse. It has been long known, but only of late years demonstrated by Dr. 

 Semper, and more recently by Professor Brooks, that spermatophores are developed by 

 the male (PI. LXXX. figs. 1, 2; PI. LXXXI. figs. 3, 4), and at certain periods when 

 required are liberated ; that these are taken up and held until required, probably only 

 for a limited period, and then projected and retained inserted in the female until the 

 ova are impregnated, as shown on PL LXXXI. fig. 1? and 2$. Since the petasma exists 

 in all those Macrura which are known to impregnate the females by means of sper- 

 matophores, it is fair to assume that this organ, which shows a remarkable correlation 

 of parts in relation to a special function, fulfils the office in a manner nearly as suggested. 

 In the males of many genera, and in the females of most of the Macrura that 

 belong to the Phyllobranchiata, there is commonly present, on the inner margin of the 

 inner branch, a long, blunt, style-like appendage, that I have named stylamblys, the apex 

 of which, instead of being sharp, is crowned with numerous small hooks with enlarged 

 points, which have been termed cincinnuli. The hooks are similar to those attached to 

 the inner margin of the petasma on each side. 



The Second Pleopoda. — The second pair of pleopoda is generally a modification of 

 the type of the first, in the direction of those that are posterior to it. The branches are 

 more normal in form, but the outer carries a stylamblys that is furnished with 

 numerous small hooks or cincinnuli. In some genera, as Sicyonia, the inner branch is 

 developed into an imperfect petasma (PI. XLIII. fig. 2q). In Penseus serratus the inner 

 branch, instead of being a broad and thin membranous plate, is long and narrow, some- 

 what like the outer one, and is furnished at the base with two globular organs 

 (PL XXXVII. fig. lq). 



In Callianassa and its near ally Cheramxis (PL I. fig. 2q) the first pair of pleopoda 

 is generally absent, or reduced to a rudimentary condition ; the second and third are 

 long and slender, the inner ramus being cylindrical and biarticulate, while the outer is 

 long and slender, and also biarticulate, the first joint being extremely long, and the 

 distal one extremely minute ; but this condition belongs more to the female than to the 

 male, in which they are smaller and more simple (PL VIII. figs. q% and q$ ; PL XIX. 

 figs. q% and q$). These distinctions are common throughout the Synaxidea, as well as 

 in many of the aberrant genera. 



In the Phyllobranchiata, the inner exists as a submembranous branch, somewhat 

 like that of the Dendrobranchiata, but it differs in the two sexes, being a little broader 

 in the males, and having the margins free from cilia. It varies in different genera or 

 sometimes even in different species of the same genus, as may be seen in Nemato- 

 carcinus, in which it ma)?- be compared with the same organ as seen in Oplop>horus. 



