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



in Ascorhynchiis miniitus, one packet only on each ovigerous leg. I lielieve, however, 

 that cases are by no means rare in which two or even three packets are formed on one 

 ovigerous leg. The packet is placed round the leg, and in some species {Nymiihoii 

 hrachyrhynchus, Hoek, e.g., PL XIX. fig. 1), it may be easily brushed off. In other 

 species, however, Nymphon robustum, Bell, for example, this is by no means so easy, the 

 surface of the joints of the ovigerous legs being furnished with numerous hook-like 

 spines. 



Every egg in the packet has its own membrane, a very thin and structureless tunic. 

 The size of the packets is very different. It varies greatly with the size of the animal, 

 but is different also in diflerent specimens of the same species. The size of the egg 

 seems to be constant for CA'^ery species ; consequently the size of the packet will depend 

 on the number of eggs in each j)acket ; and the age and the condition of the female will, 

 of course, influence this. 



The egg of Nym2)hon brevicaudatum , Miers, measures 0'5 or 0'7 mm. ; when in the 

 first stages of development it is nearly globular (0'6 x 0"6 mm.), afterwards oval (0'5 x 0"7 

 mm.). The number of eggs in each packet varies between fifty and sixty. The egg 

 of Nymphon fuscum is a great deal smaller (0"15 or 0"12 mm. The eggs oi Nymphon 

 hrachyrhynchus are about 0'55 mm. and even in a much advanced stage of development 

 nearly globular. Large packets of the latter species do not contain more than fifty eggs, 

 and the dimensions of these packets vary between 3"14 x 1'85 mm. and 2"3 x 1'6 mm. 

 The egg of Nymp)hon brevicoU a ni has a diameter of 0"2G mm.; the number of eggs in a 

 packet is in this species about ninety. Fig. 2 on Plate XIX. gives a section of a 

 packet of eggs of this species. The colours are those which are seen when the 

 object is coloured with picrocarmine, and the figure is half in outline ; every egg is seen 

 to be placed in a cavity formed by the cement which solders the eggs together (c), and 

 coloured distinctly red by the picrocarmine. The large opening (o) in the centre is 

 that occupied by the ovigerous leg ; the small holes {s, s) are those which are left between 

 the eggs when soldered together. On the outside mud and sand particles adhere to the 

 packet (m). 



So far as I know, Dohrn is the only author who has published observations on the 

 cleavage of the Pycnogouid egg ; ^ but as the method of making sections of such very 

 small eggs was not yet in use when he published his paper, and could not, therefore, 

 he applied by him, I might reasonal^ly have expected to see much more than he did, by 

 availing myself of this method of recent embryology. Yet my researches in this respect 

 were not very successful, owing at least partly, I believe, to the condition of the material 

 I studied. Ever)^ one will acknowledge how necessary it is, especially in embryological 

 researches, to study fresh and also very rich material ; now the Challenger Pycnogonids 

 had been six or seven years in alcohol before I studied their eggs, and, moreover, the 



' A. Dolirn, Ueljer Entwicklung unci Ban tier Pycnogoniden, Jenaische Zeitschrift, Bd. v., 1869. 



