PYCNOGONIDA. 



23 



of the excretory duct and thorn in contradistinction to Barana Castclli. Hoek, in Nouv. etud. 

 Pycnog. , 1881, draws the gland with excretory duct and thorn in Ammotkea longipes, pi. XXX, 

 fig. 40, and in Pycnogonum littorale, pi. XXX, fig. 45, as well as the gland alone in Nymphon gallicum, 

 pi. XXX, fig. 43. 



The descriptions and figures of Dohru, as well as most of those of Hoek do not very much 

 resemble those given by me; but I suppose that they generally represent a younger stage in the 

 development of the gland, whereas my figures, especially of the larva of Nymphon grossipes , pi. I, 

 fig. 22, and those by Hoek of Nymphon longicoxa, Report Pycnog. <• Challenger , pi. XX, fig. 5, which 

 figures are very much alike, show the fully developed stage. 



Morgan, in Contrib. Embryol., 1891, has drawn the byssus-gland in the larva of Tanystylum 

 orbiculatum, pi. IV, fig. IX, in a shape most resembling my figure of the gland in Nymphon grossipes. 

 Else Morgan does not mention the gland at all. 



I have been rather long in speaking of this gland, partly because it seems to me to have 

 hitherto been somewhat overlooked , and partly because I suppose it to have some morphological, 

 systematic importance, compared with the poison-gland in the corresponding pair of limbs in the 

 Arachnida. Possibly it might also be compared with the gland which Dohru has described by the 

 name of secretory organ-, and which he mentions as occurring in the palps and the ovigerous legs, 

 or, where these limbs are wanting, in the corresponding metameres. I think at all events this com- 

 parison to be more obvious than the comparison with the sexual glands; comp. Dohrn, Pautop. Golf. 

 Neap. 1881, his Excretionsorgane and the following paragraph, Geschlechtsorgane und Entwiekel- 

 ung , p. 63 seq. 



The development of the second larval stage begins with the growing of the 

 hindmost segment of the trunk, and the separation of a foremost ring with the first 

 pair of hind limbs, or ambulatory legs, upon which in a similar way the second and 

 third pairs of ambulatory legs are separated, while the fourth pair and the caudal 

 segment are seen behind as a three-cleft appendage. At the close of the development 

 of this stage the embryonal legs have fallen off, but the imaginal limbs and fore- 

 limbs, the palps and ovigerous legs, have not appeared, if they appear at all. Only 

 very rarely the chelifori fall off already on this stage. The byssus-gland is kept till 

 the development of the stage is finished. 



The development of the second stage does not take place at once, but through more or fewer 

 castings of the skin, and in such a way, that sometimes a greater, sometimes a smaller interval is 

 found between the origin and the development of each of these three pairs of ambulatory legs, while, 

 however, the consecutive order is kept. Perhaps it may be called a little arbitrary to limit the second 

 stage in the way we have done here, as in some species so great a pause may occur during the 

 stage, especially after the development of the second pair of ambulatory legs, as is the case in Psett- 

 dopallene circularise that we might as well place the limit of a larval stage after the development of 

 the second pair as after that of the third pair; in most Pycnogonid-larvae , however, the development 

 is evenly advancing, till the third pair of ambulatory legs have been developed. 



As in the preceding section the genera Pallenc and Pseudopallene were especially mentioned 



