22 PYCNOGONIDA. 



from it, are Nymphon, Pycnogomim, Pseudopallene, and Pallenc. In the last-mentioned genus, however, 

 I have in Pall, bremrostris found, in stead of a single thread originating from the common gland, a 

 bundle of seven, rather short, somewhat curled threads each issuing from an excretory duct of its 

 own, pi. I, fig. 16 and 17. I have seen no gland from which any of these threads might arise; but I 

 think it also probable, in comparison with what Hoek has found in Nymphon ha mat u in, what I shall 

 presently recur to, that each of the seven threads arises from a cell of its own. In Plioxichilidium 

 femoratum I have found no trace of these glands, nor of their thorns and threads; the threads drawn 

 on pi. I, fig. 4, are the outermost joints of the embryonal legs, which are prolonged in a bristlelike 

 manner, and probably replace the wanting byssus-threads; this larva, with its parasitic way of living, 

 has no use for the hooks, to which in the other Pycnogonida the outermost joint of the embryonal 

 legs has been transformed. In Paranymphon spinosum 1 }, pi. II, fig. 22 24, I have found indistinct 

 traces of the gland and excretory duct, and the thorns were long and closed. In Zrfcs Iiispidus, pi. II, 

 fig. 27, I have found a distinct gland, but no excretory duct from it, and also here the thorns were 

 closed. It may be possible that in the two last-mentioned cases a reduction of a commonly occurring 

 organ has taken place, as it would seem to be natural in Phoxichilidium; but it may also be supposed 

 that we have here a stage of transition from a simpler organ to the more perfect byssus-gland. 



Dohrn and Hoek have already earlier described and drawn this gland, and Dohrn espe- 

 cially, in Bau u. Entwick. Arthrop. 1870, has from the larva in the first stage of Achelia lavis (= 

 Ammothea lavis) Taf. V, fig. 7, given a figure of the gland with its excretory duct and a secretion- 

 thread (byssus) projecting from the long, pointed, hollow thorn, but from Pycnogomtin littoralc in a 

 similar stage only the hollow thorn, he, as it would appear, not having seen the thread, not to speak 

 of the gland. In the text he, when speaking of Achelia Icevis, describes the gland rather copiously, 

 but says nothing of its use or importance, I.e. p. 141 seq. Hoek, in Report Pycnog. Challenger, 

 1881, draws this gland in Nymphon brevicollum and N. longicoxa, pi. XX, fig. 2 and 5, and names it 

 in the explanation to the plates Spinning apparatus in the mandible. In another Nymphon', N. 

 hamatum, pi. XX, fig. 3 and 4 he draws, instead of the common gland, a whole heap of single miliary 

 gland cells each cell with its own secretion-thread. No doubt this last form of glands with its threads 

 corresponds to the bundles of threads I have mentioned in Pallene brevirostris; and as in the last- 

 mentioned species the gland was different in structure from that of the other species of the same or 

 of nearly related genera, so is also the structure of the gland in Nymphon hamatum peculiar, compared 

 with that in all the many species of Nymphon, from which the gland is known. Hoek in his text, 

 I.e. p. 141, compares the secretion-threads to the byssus-threads of the Lamellibranchiata, which com- 

 parison I have found so appropriate that I have given to the gland itself the name of byssus-gland. 

 Dohrn generally draws the byssus-gland of the larvse of which he gives figures, but he does not 

 always indicate it by special letters; when he does so, he gives the letters HD, which in the explan- 

 ation to the plates are rendered as Hautdrusem , and DHD, which are rendered as Ausfiihrungs- 

 gang der Hautdriisen. In the text they are mentioned in the section entitled, Geschlechtsorgane 

 und Entwickelung, especially on p. 70 seq., and here Barana arcnicola is also pronounced destitute 



') Cp. the note on p. 14. 



