I4 PYCNOGONIDA. 
måles — tous les trois paires), les segments thoraciques se développent successivement au bord posté- 
rieur du corps, et aussitåt un nouveau segment formé, une paire de pattes se montre également 
comme excroissances latérales de ce segment. Quand quatre paires de pattes se sont ainsi développées 
aux quatre segments thoraciques (notons que Pordre de développement des pattes correspond tout å 
fait å leur rang dans le corps de P'animal adulte), ”excroissance terminale se change en un abdomen 
plus ou moins rudimentaire.s» 
Morgan has given a little series of essays on the Pycnogonida, of which especially the last 
one may be mentioned, entitled: «A Contribution to the Embryonalogy and Phylogeny of the Pycnogonids» 
(1891). In this essay Morgan gives the development of Proxichilidium maxillare ([= femoratum 
Rathke?|, of Pa//ene empusa, and of 7anystylum orbiculare.…. He has more than his two above men- 
tioned predecessors paid attention to the first development of the embryo, an examination that Krøyer 
did not enter upon at all, and gives furthermore a very handsome series of the developmental stages 
of the larva, especially the larva of 7anystylum; on the other hand I do not think his represen- 
tation of the larval development of Fa//ene empusa to be correct. In his introduction l.c. p.2 Morgan 
says: «For many reasons the present paper attempts in no way to give a complete answer from the 
embryonal side. The very great difficulties of a suitable technique had slowly to be overcome, and 
the time at command prevented a detailed description of the different organs arising from the germ- 
layers, so that much remains that might be done,» but nevertheless his essay is a. very important 
advance in our knowledge of the development of these animals, as also his representation of the 
structure and development of the eye in the Pycnogonida is rather exhaustive. 
Passing now to my own description of the larval development I have to begin with the usual 
complaint of not having had fresh material at my disposal; but on the other hand the Ingolf-Expe- 
dition has brought home so rich a material well preserved in spirit that I suppose I shall be able to 
give a more detailed and continuous description of the different stages of development in the larva. 
I have been able to follow the development for a shorter or longer way in a considerable number of 
Pycnogonida, belonging to the different families and genera as Wymphon grossipes, Sluiteri, elegans, 
longitarse, robustum, spinosum, macronyx; Paranymphon spinosum-); Zetes (Eurycyde) hispidus; Pseudo- 
pallene circularis and spinipes; Pallene hastata and breværostris; Phoxichilidium femoratum; Pycnogonum 
littorale, altogether 7 genera with 15 species. The species, the development of which I have most 
complete, are Wymphon grossipes, N. robustum and Pseudopallene circularis, of which three species the 
first and the last are those that have been particularly examined by Krøyer; but besides corrobo- 
rating most of his statements and drawings (I have partly examined his original pieces) I have also 
been able to increase and partly to correct some of them, which corrections especially apply to Psew- 
dopallene circularis. 
The segmentation, yolk-division, of the Pycnogonid ovum is complete, some- 
times equal, sometimes unequal. 
For the correctness of this thesis I must refer to Morgan, Contrib. Embryol., 1891, and I 
have nothing to add. It is, I think, to be supposed, as Morgan does 1. c. p. 23, that the difference 
between equal and unequal segmentation, which latter is also continued in the difference between 
1) In pl. II, fig. 22—24 are wrongly called spinipes in stead of spinosum. 
