﻿J, PYCNOGONIDA. 



males — tons les trois paires), les segments thoraciques se developpent siiccessivement au bord poste- 

 rieur du corps, et aussitot un noiiveaii segment forme, une paire de pattes se moiitre egalement 

 comme excroissances laterales de ce segment. Quand qnatre paires de pattes se sent ainsi developpees 

 aiix qnatre segments thoraciqnes (notons qne I'ordre de developpement des jjattes correspond tout a 

 fait a leur rang dans le corps de Tanimal adulte), Texcroissance terminale se change en nn abdomen 

 plus on moins rudimentaire. » 



Morgan has given a little series of essays on the Pycnogonida, of which especialh' the last 

 one ma}- be mentioned, entitled : A Contribution to the Embryonalogy and Phylogeny of the Pycnogonids-? 

 {1891). In this essay Morgan gives the development of Phoxichiliduiw viaxillarc [= fcmoratum 

 Rathke?J, of Pallcnc ciiipusa, and of Ta)iystyhnn orbiailarr. He has more than his two above men- 

 tioned predecessors paid attention to the first development of the embryo, an examination that Kroyer 

 did not enter upon at all, and gives furthermore a very handsome series of the developmental stages 

 of the larva, especially the larva of Tanystyht ni \ on the other liand I do not think his represen- 

 tation of the larval development of Pallcnc cmpusa to be correct. In his introduction I.e. 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 slowl\- 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 essa\- 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 m\- own description of the larval development I liave to begin with the usual 

 complaint of not having had fresh material at \\\\ disposal; but on the other hand the Ingolf-Expe- 

 dition has brought home so rich a material well preserved in spirit tliat I suppose I .shall be able to 

 give a more detailed and continuous description of the different stages of development in tlic larva. 

 I have been able to follow the development for a shorter or longer wa\- in a considerable mimber of 

 Pycnogonida, belonging to the different families and genera as Nymphon grossipes, Sluitcri, elcgaus, 

 longitarsc, robtishiiii , spiiwsiiii/, niacronyx; Paranyiiiphoti spmosu)n^)\ Zetes {Eurycydc) /iispidns\ Pscudo- 

 pallcnc circularis and spiiiipcs; Pallcnc hastata and brcvirostris; Phoxichilidium fcmorafnm\ Pycnogonuin 

 littoralc, altogether 7 genera with 15 species. The species, the development of which I have most 

 complete, are Ayniphon grossipcs, iV. robnshtm and Psendopallcnc circularise of which three species the 

 first and the last are those that have been particularly examined by Kro\-er; but besides corrobo- 

 rating most of his statements and drawings (I lia\e parth' examined his original pieces) I have also 

 been able to increase and partl\- to correct some of them, which corrections especially apply to Pscu- 

 dopallenc 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 i.s, I think, to be supposed, as Morgan does I.e. p. 23, that the difference 

 between equal and unequal segmentation, which latter is also continued in the difference between 



ij In pi. II, fig. 22—24 are wrongly called spinipes in stead of spiuosuni. 



