﻿PYCNOGONIDA. 31 



is shown by the series of larval forms, given in the following figures 8 — 11, and 16—17 of Psciido- 

 pallfijc spiiiipcs and circii/ari.<; , as well as of Pallviir brrvirnstris\ as thc\-, however, belong to the se- 

 cond larval stage, tlie\- will be mentioned more in detail in a following section. It may be possible, 

 of course, that I can have overlooked rudimentary larval legs; but in a somewhat later stage of the 

 same species I have seen no trace of these legs either, and as, in all places where I have observed 

 them, thev have only appeared as one or two pairs of short, inarticulate jDrocesses, I am inclined to 

 suppose that here they have been quite absent. Of still less importance is the peculiarity that the 

 foremost pair of ambulatory legs have begun to appear so earl\-, before the chelifori were quite 

 developed, and before the byssus-gland was formed. Tlie two genera mentioned here must be supposed 

 to pass a great part of the second larval stage in the egg-shell. 



Morgan, Contrib. Embryol. 1S91 has not in Pallciic niipiisa seen any trace of the foremost pair 

 of the embryonal legs, though he has seen some trace of the second pair; at all events I understand 

 the following quotation in that wa\'. I.e. p. 14. On the sides of the body, just in front of the first 

 pair of ambulatory legs, are a pair of projections, one on each side. These are the beginning of the 

 third pair of limbs — the ovigerous legs. I have seen no traces of the second pair of appendages in 

 the ontogeu}- of Pallene -. 



In the basal part of the chelifori is most frequently found a large gland, the 

 byssus-gland, with an excretor\' duct opening throngli a shorter or longer hollow 

 thorn in the fore-margin of the said basal part. 



The occurrence of a large gland in the chelifori has already been mentioned by Dohrn and 

 Hoek, who have also gi\-en descriptions and figures of it; b\' Morgan it is only drawn in the che- 

 lifori of Taiiystvlum oybicnlatuiii\ cp. the following. 



This gland, the byssns gland, is most frecpienth- distinctly conspicuous, and through the 

 epidermis it is seen to consist of a circle of large glandular cells gathered round a hollow, or reser- 

 voir, from which an excretory duct is seen to lead to the inner fore-end of the basal part of the 

 cheliforus, comp. the enlarged figure of the fore-end of the lar\a of Xyiiip/ioii grossiprs, pi. I, fig. 22. 

 In Nyinplion clrgiuis^ pl-H, fig- 16, I have found the gland to be almost as distinct and of the same 

 structure; while it was far less distinct in Xymplioii loiigitarsc, pi. II, fig- 19 — 20, Xyiiiplion robtistum^ 

 l^l. II, fig. 6, Xyi/ip/ioi! n/acroiiyx, pi. II, fig. n, and in Xy/Jip/iou sp/i/osiiiii, pi. II, fig. 13; but j^ossibly it 

 was not quite developed, and so was not so well preserved in the spirit. The excretory duct opens 

 into the basal end of a .shorter or longer hollow thorn, through the point of which the gland-.secretion 

 is produced as a very thin thread of a considerable length. The thread, which stains strongly (I have 

 in all instances used picro-carmine), is easily seen, and is also to be seen in my figures of the larvte. 

 The development of the gland begins very earh- in the embr\-t)nic stage on the border of the basal 

 end of the cheliforus and the corresponding metamere, but it is uot finished until later in the first 

 larval stage, when the larva has left the egg wholl\-, or, at all events, with the fore part. The length 

 of the excretory thorn varies very much; generally it is short or even very short, but it can, as in 

 Pycnogouuni liftora/r, gain a verv considerable length, about the length of the embryi)nal legs, cp. pi. I, 

 fig. 3, where, however, the limit between the thorn and the free thread, which limit is difficult to see, 

 has not been indicated. The genera, in which I have found a distinct gland with a thread ari.sing 



