PYGNOGONIDA. 



J 3 



the belly of the mother' (the father it ought to be); sometimes the yolk is consumed, and then the 

 young one has to find its food. 4 In the third stage the larva gets the fourth and last pair of (ru- 

 dimentary) feet. The two preceding pairs (the three preceding must be meant) are very much devel- 

 oped. The maxillae (i.e. palps and ovigerous legs) on the contrary, are still, in the species where 

 they are found, quite rudimentary. 5 After a new casting of the skin the animal nearly gets its 

 permanent shape, although the length of the body and the limbs is altered not a little. 



Doh r 11 in a couple of works has given important contributions to the history of development, 

 first in his: Untersuchungen iiber Bau und Entwickelung der Arthropoden > (1870) in the second sec- 

 tion of which, with the sub-title Ueber Entwickelung der Pycnogoniden , he treats of the develop- 

 ment of the larva of Pycnogonum litterale, Achelia hrvis and Phoxichilidium sp. Still more important, 

 however, is the contribution, he has given in the monograph entitled: Die Pantopoden des Golfes 

 von Neapel (1881), in which, besides descriptions and figures of many different genera as Barana, 

 Ammothea, C loft nia, Phoxichilus , Phoxichilidium and Perflate, he gives an account of the larva? known 

 to him, and their development I.e. p. 69 — 80. The principal progress in our knowledge of the devel- 

 opment given by Dohrn is that he justly shows how Kroyer has been wrong in his interpretation 

 of the development of the two foremost pairs of ambulatory legs, as if those pairs had arisen by an 

 uninterrupted development of the two hindmost pairs of limbs in the first form of the larva, the em- 

 bryonal legs as I have called them. Kr oyer's error is, I suppose, principally due to the fact that 

 in the very young larva of Pallene (or Pseudopallene] these limbs are almost or entirely wanting, and 

 so Kroyer has taken the two foremost pairs of legs (i.e. ambulatory legs) to be corresponding to the 

 two foremost pairs of legs (i. e. embryonal legs) in the larva of the other species. In the following I 

 shall again recur to this subject. 



The works on the Pvcnogonida by Hoek are well known. The two most important are: 

 Report on the Pvcnogonida in the Voyage of H. M. S. Challenger (1881) in which he on the 

 plates XIX and XX represents the larva? from their earliest development; and next his «Nouvelles 

 etudes sur les Pycnogonides (1881) where on pi. XXX the different larvae are represented. Besides 

 figures of well known forms, as Phoxichilidium, Ammothea and Pycnogonum, he especially draws 

 different species of the genus Nymphon. In the lastmentioned treatise, I.e. p. 481 seq. Hoek gives 

 the results of his examinations in the following way: v Void en pen de mots le resultat auquel je suis 

 arrive: on trouve toujours, a quelques exceptions pres, comme premiere forme larvaire, un animal avec 

 trois paires d'extremites, dont la premiere se termine en une piuce et dont les deux suivantes sont 

 formees de deux articles et se terminent par des griffes allongees (larve Protonymphon). Les deux 

 deruieres paires d'extremites sont -- comme la premiere paire — des appendices simples, e'est-a-dire 

 qu'elles ne sont pas divisees en deux branches comme celles des larves Nauplius. La bouche est 

 placee a la fin dune excroissance de forme cylindrique ou conique, qui est implantee entre la pre- 

 miere et la seconde paire d'appendices: cette excroissance, e'est la trompe, qui au moment de l'eelosiou 

 de la larve est toujours tres courte, mais possede deja cette forme conique ou cylindrique. 



La maniere dont l'animal adulte se developpe de cette forme larvaire est des plus simples. 

 Tandis que les trois appendices originaux se metamorphosent dans les trois paires d'appendices 

 cephaliques ou disparaissent (soit une, soit deux, soit — et ceci n'arrive jamais chez les individus 



