REPORT ON THE PYCNOGONIDA. 15 



The mandibles in some genera are two-jointed {Nymplion, Pallene, &e.), in others 

 three-jointed {Phoxichilidium). As a rule the second or third joint terminates in 

 a pair of pincers, with a movable and an immovable claw. Now there are genera, some 

 species of which show the mandibles small, yet furnished with true pincers, whereas 

 other species of the same genus show the mandibles in a mucli more rudimentary state, 

 as if, for instance, represented only by a single joint terminating abruptly [Ascorhynchus 

 glaher, Hoek, and A. minutus, Hoek). In other genera the mandibles are in the adult 

 animal always rudimentary, represented only by short stumps {Lecithorhynchus, Bohm, 

 Oorhynchns, Hoek, &c.) ; whereas in a fourth category the mandibles have totally 

 disappeared {Colossendeis, Phoxichilus, Pycnogonum, &c.). Among the specimens of a 

 species of one of these genera {Colossendeis gracilis, Hoek), dredged during the cruise of 

 H.M.S. Challenger, I have, however, found one specimen furnished with a pair of 

 distinctly three-jointed mandibles, terminating in a pair of pincers ; and this specimen 

 was the largest of the three obtained. 



The palpi when present show very different numbers of joints. Thus there are 

 only three in Pefhredo, five in Nymiilion and Discoamchne, eight in Achelia, nine 

 in Ammothea and Corniger, ten in Ascorhynchus, Colossendeis, &c. The palpi have 

 disappeared in the genera Pallene, Phoxichilidium, Phoxichilus, Pycnogonum, &c. 

 In Phoxichilidium they are as a rule still represented by rounded lateral processes 

 placed at both sides of the front part of the cephalothorax, whereas Bohm has observed 

 a specimen of Pallene furnished with rudimentary, yet distinct two-jointed palpi. 



The third pair of appendages, viz., the ovigerous legs, are never wanting in any 

 species of Pycnogonids. Among the Pycnogonids of the Challenger, there is not even 

 a single specimen without ovigerous legs ! As a rule they are ten-jointed ; the first three 

 joints are extremely small, the two following are the longest of all, the sixth joint is a 

 great deal shorter, the last four joints are much shorter still, the tenth joint as a rule 

 is furnished with a claw. In some genera {Colossendeis, e.g.) the fifth joint is small, 

 the sixth as long as the fourth joint. In those genera, where a certain tendency is 

 observed to drop their cephalic appendages, the ovigerous legs share this fate only to a 

 small extent. As the functions of the ovigerous legs are twofold, one being to bear the 

 eggs, a function only accomplished by the male,' the other to serve as an organ of feeling, 

 also, in all probability, of seizing the food, and as the latter of these functions is almost 

 identical with that of the other cephalic appendages, it is quite natural, I believe, that, 

 whereas the males are never seen without these appendages, they are wanting in the 

 females only of those genera which have also lost their other cephalic appendages. 

 Finally, it is evident, that the males of those latter genera ought to show the ovigerous 

 legs in such a rudimentary state, as to be fit only for the ovigerous function. 



DorsaUy the front part of the cephalothorax bears the oculiferous tubercle ; although 



' Hereafter I will show that this rule admits of an exception. See under Nymphon brevicaudatum, Miers. 



