EEPORT ON THE PYCNOGONIDA. 129 



by a commissure, so there is only one true testis, which has the form of a capital U. 

 From the upstrokes of this U, on both sides, those parts originate which penetrate 

 the leg, and which extend almost to the end of the fourth joint. The two jaarts of the 

 testis which run longitudinally through the body are broad and fiat ; their course is not 

 straight but rather undulated, being bent outwards whenever a lateral branch takes its 

 origin. Although the organ is placed at the dorsal side of the body and legs, the 

 male genital pores are situated ventrally towards the end of the second joint of each leg. 

 This external opening is very small and is at the tip of a distinct conical tubercle. It 

 leads into a canal which runs backwards almost parallel with the margin at the distal 

 extremity of the joint and closely adheres to its chitinous covering ; this canal runs 

 along the wall of the joint till it reaches the dorsal side of the leg, here it becomes wider 

 and turns inwards tdl it reaches the testis, which shows a small knob facing the beginning 

 of the canal. Plate XXI. fig. 11, shows these particulars; the joint is figured as trans- 

 parent, and the muscles which run from this to the following joint are to be considered 

 as removed. The outer part of the canal, from the opening for about one-fourth of its 

 length, is furnished with a thicker wall, and this shows most probably the extent to 

 which the chitinous covering of the leg is bent inward. The remainder of the canal 

 is formed of connective tissue, — at least I failed to observe an endothelial covering, — 

 lined externally by a distinct muscular layer, the fibres of which run longitudinally 

 and are not striated (PL XXI. fig. 13). 



As seen in fig. 2, Plate XVIIL, that part of the testis which penetrates the leg is in a 

 transverse section kidney-shaped ; a longitudinal duct is formed between the gland and 

 the thin tissue or membrane which it touches laterally at two points. Most probably it 

 is with the duct so formed that the canal which opens at the distal extremity of the 

 second joint is in communication. 



I have observed nearly the same structure of the male genital organs in the 

 extremely transparent species of Nymphon, to which I have given the name of Nymphon 

 perlucidum (p. 50 of this paper), and also in Nymphon robustum, BeU. Both species 

 show genital pores in the male sex, only on the two hindmost legs ; and quite in cor- 

 respondence with this observation only two pairs of lateral excrescences of the U-shaped 

 testis are to be seen. So when Dohrn says, for Pycnogonids in general, that the male 

 organs penetrate each leg and open in a round pore on the ventral side (which is, 

 no doubt, the case in all the species examined by him), he is laying down a 

 rule which admits of a great many exceptions ; for among the Pycnogonids dredged 

 by H.M.S. Challenger there are species having their male genital pores only on the 

 two hindmost legs ; again, there are some which possess them on the three hindmost 

 pail" of legs, and, finally, there are species with pores on all the legs. My doubts about 

 this point were cleared up by the observation of those species which bear their male 

 genital pores at the tip of a stout cylindrical outgrowth (species of Ainmothea, e.g.). 



(ZOOL. CHALL. EXP. PAKT. X. 1881.) K 17 



