PYCNOGONIDA. 



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

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

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

 der Pantopoden , especially p. 87 seq. 



When the yolk-division is unequal, only the foremost part of the blastoderm 

 participates in the formation of the embryonal limbs and the proboscis, while the 

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

 behind. The embryo remains wholly 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 Protonymphon ; besides from the large genus Nymphon 

 it is also known from the genera Pallene, Pseudopallene , and Zetes (Eurycyde), and I shall also be 

 able to add some new forms. It may, however, 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 Nymphon a yolk-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 H o e k with regard to Nymphon gallicum. 



In both forms this larval 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 metamere 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 Pallene. and Pseudopallene , which 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, anteriorly enclosing the single protuber- 

 ance of the proboscis, comp. my figure of the ovum of Pycnogonum littorale pi. I, fig. i. All seven 

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

 which in the embryonal 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 distinctly 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 always in the 

 larva form a chela or a pair of pincers, so that these limbs get a very great resemblance to the chelae 

 of the Arachnida. It is a matter of course that this congruity 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 have 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 part is comparatively short, and never constricted from the body; the first 



The Ingolf-Expedition. III. I. 



