﻿PYCNOGONIDA. 



on account of their peculiarity-, so we shall also here mention these genera as the last, and for the 

 same reason likewise dela\- the examination of the genus Phoxichilidium. 



The genus Xymphon., which is, together with the subgenera Boreonymphon and Chatonymphoii, 

 chiefly a palearctic form, presents by its numerous species and great extension the best opportunity 

 for European naturalists in these northern countries to make a continuous study of the development 

 of the Pycnogonid lars'ae. It is also Xymphon grossipes of which we have the most detailed represen- 

 tation, already given by Kroyer, Kundsk. Pycnog. (1845), ^^ i* i^ also this species I shall use, and, 

 with reference to my figures, pi. I, fig. 21 — 25, give a representation of its development during 

 this stage. 



On the preceding figure, pi. I, fig. 20, representing the beginning of tlie second stage, is seen, 

 besides the three pairs of embryonal limbs, also the beginning of the two foremost pairs of ambulatory 

 legs, though only slightly pronounced; but in fig. 21, which absolutely belongs to the second stage, 

 the first pair of ambulatory legs are already much developed, of about the same length as the trunk, 

 and with the last joint well developed to a bent, strong claw with two slender thorns, the auxiliary 

 claws, arising from the dorsal side near the base; the articulation of the leg, however, have not pro- 

 ceeded farther than to five joints exclusive of the claw. The second pair of ambulatory legs have not 

 been developed farther than to form a cylindrical process without any articulation or claw, neither 

 are in the body itself the corresponding segments conspicuous, which latter circumstance, perhaps, 

 may be due to a not quite good preservation. The byssus-gland , however, is now fully developed, 

 and the byssus-thread is distinctly seen to originate from the middle of the gland. In the following 

 figure, fig. 22, the fore-end of the larva has been represented much more enlarged to show distinctly 

 the structure of the byssus-gland. In the same figure the yolk-mass in the foremost part of the body 

 is also seen to consist of small particles (the micromeres?) smaller than those of the hindmost part (the 

 macromeres?), of which, however, only a small portion has been represented; a particular interspace be- 

 tween the two yolk-masses is also distinctly seen. In fig. 23 the lar\-a is represented much more devel- 

 oped, but still in the second stage; both tlie foremost pairs of ambulator\- legs are now well devel- 

 oped, all nine joints, inclusi^■e of the claw , being well separated , and the two auxiliary' claws ven,- 

 large; the third pair of legs are also rather long, four-jointed, but the last joint not yet claw-shaped, 

 and there is no indication of an\- auxilian," claws; the fourth pair of legs and the hindmost part of 

 the trunk form a solid body, while short curves behind indicate the wanting pairs of limbs; anteriorly 

 in the trunk the transverse-oval eye-knob with indistinct e\es is seen; the byssus-threads are still 

 present Fig. 24 shows the same larva from the lower side, and it shows how the yolk mass not only 

 fills the whole trunk, but also sends long processes into the three pairs of ambulatory- legs. The yolk 

 is surrounded by a distinct sheath, seen with special distinctness in the third pair of legs, and forming 

 the walls of the intestine canal during the following development Before, on both sides of the pro- 

 boscis, the embryonal legs are still seen, but they are now decaying, the matrix, or pulp — as it was 

 called in the old times — shrinking, and being consumed (?). In fig. 25 the embr^'onal legs have been 

 represented still more enlarged, by which means also the epidermis of the legs is distinctly seen in 

 contradistinction to the pulp, and where it is seen to have preserv^ed its former size and firmness, 

 onl}- the point of the outermost joint being a little retracted; an e^•en shrinking or resorption of the 



