﻿PVCXOGOXIDA. ,. 



embryonal legs, or, at all events, of their exoskeleton is accordingly out of the qncstion, we must sup- 

 pose them to be thrown off at once. 



In his first essay, vOm Pycnogonidernes Forvandling (On the metamorphosis of the Pvcnogo- 

 nida) 1840, Kroyer already gives a rather detailed description of this stage, but of the embrvonal leo-s 

 he has onh- seen one pair; his words are (I.e. p. 303): -Between the chelifori and the first pair of feet 

 I have sometimes seen projecting on the side a little process, fig. 3c, appearing to consist of onlv 

 two joints and of a length of abt. ' ,3'" (Danishi; after its position I think it must be taken to be the 

 first trace of the palps. The interpretation by Kroyer of this little organ , to be sure, was not 

 correct; but to this question I shall recur in the following, in the section on the /^stiee/opalln/r-laTva.; 

 here I shall only add that the figure of the larva it.self, fig. 3 ^?, is bad, and couseqnentlv the repro- 

 duction of this figure and other ones from his plate III, as the\- are given after the drawings 

 by Thornam, in the work of travel of Gaimard (1849) pi. 39, fig. i «— ^^ must be considered as a great 

 progress. In the work of tra\el the new principal figure, fig. i «', resembles verv well our fig. 23, and 

 the pointed thorns or hooks with which also the limbs behind the chelifori here are seen to end, agree 

 very well with the outermost joint or hook of the embryonal legs, but not with the imaginal fore 

 limbs in any stage whatever. 



The second species the development of which I have been able to follow, is Xymphon robiisluiii, 

 and I shall here describe the second stage, referring to my figures, pi. II, fig. 2 — 6. A peculiaritv of 

 this species, when compared with most of the other species, is the long time, during which the lar\-a 

 remains confined in the egg-shell, or the egg-membrane and cast-off lar\al sloughs'). The first stage 

 of the larva in m\- possession is the second stage, shown in fig. 2: here the larva is seen enclosed behind 

 by two membranes besides the egg-shell, and that it is not onl\- the trunk which has cast off its 

 slough, ma\- be seen from the proboscis, of which one cast-off slough is seen enclosed in the other, as 

 I have shown it more distinctly by a special figure, fig. 3. In fig. 2 otherwise, all four pairs of ambu- 

 latory legs are seen in a course of de\elopment, the first pair as usual farther proceeded than the 

 others, but still only with slight constrictions indicating the beginning articulation. The seginentation 

 of the trunk is already here discernible, and it may also be obser\-ed that the first pair of embryonal 

 legs more than nsualh- are distinguished by being earlier de\-eloped and thicker than the second pair; 

 as it is the case with the first pair of ambulatory legs, the old slough is also here seen looseh' wrapping 

 the first pair of embryonal legs. In fig. 4 showing a stage a little more advanced, the proboscis as 

 well as the abdomen is seen lying in the two last sloughs; the second pair of ambulatory legs have 

 here grown comparativel\' more than an\- of the other limbs; besides the byssus-threads are now 

 secerned. In fig. 5 and 6 the development has proceeded still farther, tlie two foremost pairs of am- 

 bulatory legs are completely articidated, while the third pair is still nnicli shorter than the other.s, 

 and the articulation not quite finished. In fig. 6 showing the lar\a from the lower side, the byssus- 

 gland is developed. Tlie auxiliary claws are as a rule very small though quite distinct, which feature 

 is characteristic of the species. 



Of Xyiiiplion ii/acroiiyx I possess, besides the lar\a on the first stage mentioned in the fore- 



■| It is also this spucics that for a 1oii^v;<.t lime lliaii any otliiT rycnogoiiiil cliniis to the ovigcrous legs of the father; 

 comp. the representation of this fact by Hoek. Pycnog. Willeni Karonts , iSSi, Taf. II, fi.g. 55. 



The Ingolf.E.\pctJitioii. III. 1. 4 



