﻿PYCNOGONIDA. 



Pycnogonida in a so-called natural system (phj-logenesis), several authors, and especially Dohrn, 

 having- thought to find the Nauplius-type in it, a conception that Dohrn, however, as i-s well known, 

 has again abandoned, comp. his Pantopoden des Golfes von Neapel (1889), the section Phvlogenie 

 der Pantopoden , especialh' p. 87 seq. 



When the yolk-di vi sion is unequal, only the foremost part of the blastoderm 

 participates in the formation of the embr\unal limbs and the probosci s, while the 

 hindmost part of this latter with enclosed macromeres appears as a bag-like dilation 

 behind. The embryo remains wholl\' or partly in the egg, or, if it leave it, the em- 

 bryo remains at or on the father. 



This larva which is to be regarded as the close of the first larval stage, has hitherto been 

 drawn from a less number of genera than the Proton\-mphon ; besides from the large genus Xympliou 

 it is also known from the genera Pal/r/ir, Pscudopanriir, and Zcies (Eiirycydc), and I shall also be 

 able to add some new forms. It ma>-, howe\-er, sometimes be questioned whether this larval stage 

 here is to be regarded as Protonymphon or not. Thus for instance in the hitherto known species of 

 the genus Xyii/p/io)/ a >-olk-sack is always found at the close of the first larval stage, but this sack 

 sometimes is so very small, that one may be tempted to regard the larva in this stage as Protonym- 

 phon, as has been done by Hoek with regard to Xyiiipltoii gaUiciiin. 



In both forms this 1 a r \- a 1 stage begins with a contemporaneous development 

 of the three pairs of embryonal limbs, i.e. the chelifori and the embryonal legs, each 

 pair of the limbs representing its m e t a m e r e with the ganglia, and besides an inter- 

 jacent process with an oral orifice at the point, i.e. the proboscis. 



A peculiar position is here occupied by the genera Pallciir and Psrudopalloic , whicli will be 

 bespoken more in detail at the close of this section. 



The embryonal limbs accordingly appear at the same time as three pairs of large, flat protuber- 

 ances, warts, or processes on the under side of the blastoderm, anteriorh' enclosing the single protuber- 

 ance of the proboscis, comp. m\ figure of the o\um of Pyciwgoi/uiii littoralt' pi. I, fig. 1. All seven 

 lumps are prolonged in a tubiform manner to lengthy processes, pi. I, fig. 2, the foremost free ends of 

 which in the emljryonal limbs are segmented by two consecutive segmentations. Of these three pairs 

 of limbs the foremost pair, the chelifori, are almost from the beginning larger than the others, and 

 grow disproportionately, when compared with those, and the hindmost part, the part arising from the 

 trunk, is also more or less distincth' constricted from this as an independent joint, the scape. Further- 

 more the fact has also to be mentioned that the two terminal joints of the chelifori alwa3'S in the 

 larva form a chela or a pair of pincer.s, so that these limbs get a very great resemblance to the chela; 

 of the Arachnida. It is a matter of course that this congrxiity with the said organ of the Arachnida 

 must be carefully taken into consideration when the question is of the systematic affinity of the two 

 groups; another question, however, is, how much importance we shall ha\e to attach to it. Finally 

 is here to be mentioned the gland which is most frequently found in the basal part or the scape of 

 the chelifori, and the shorter or longer thorns, arising from this joint. 



The two hindmost pairs of limbs, the embryonal legs, are uniform , always much smaller than 

 the chelifori. Their basal jjart is comparatively short, and ne\er constricted from the body; the first 



The Inj^olf-Kxpedition. III. i. O 



