l6 PYCNOGONIDA. 



development taking place before this act, is reckoned to the embryonal stage, but that I cannot agree 

 with this view. As the embryo, however, in the different Pycnogonida, breaks the egg shell some- 

 times after a shorter, sometimes after a longer development, nay, sometimes not even, until all the 

 limbs, the ambulatory legs included, have been developed, it will be understood that Korschelt and 

 H eider, Lehrb. Entwick. wirbell. Thier. 1890, in their large, well known text book can say of the 

 Pycnogonida that only die meisten Pantopoden entwickeln sich mittelst Metamorphose, I.e. p. 662, 

 as if there were any important difference between the different Pycnogonida; Dohrn, Pantop. Golf. 

 Neap. 1881, even says I.e. p. 77: Pallene hat die gauze Larvenentwickelung vollkommen unter- 

 driickt, das junge Thier, welches die Eischale verlasst, besitzt bereits alle definitive Extremitaten, 

 wenn auch noch nicht in definitiver Gestalt. On the following page we find: Wenn der Embryo 

 seine Reife erreicht hat, gleicht er in vielen Beziehungen der Larve von Phoxichilidium , welche den 

 Hydroidpolypen verlasst. In my opinion the peculiarity in Pallene cmaciata, the species mentioned 

 by Dohrn, is only to be found in the fact that the larva completes its development in the egg, in- 

 side the egg shell; and that this fact is not to be understood as something general in the genus, but 

 only as a peculiarity in this species among known forms I infer from the fact that in another Pallene- 

 species, Pallene hastata, I have found all larvae free with only three pairs of developed ambulatory 

 legs, pi. I, fig. 1819. In tne nearly related genus Pseudopallene I have even found the larva free in 

 its first stage with the two foremost pairs of ambulatory legs not yet quite developed, pi. I, fig. 8. In 

 the following I shall enter into further details as to this fact Also in other genera, for inst in Nym- 

 phon, it may be found in the different species that the larvae leave the egg shell sooner or later, with- 

 out any other difference in the course of development. It is quite another thing that a good bound- 

 ary really exists, but it can as usual be placed at the origin of the first larval form, here according- 

 ly it is to be applied to the form that has been called Protonymphon* (Hoek; or the Pantopod- 

 larva (Dohrn). 



Already in the introduction to this section on the larval development, I spoke of the usual 

 misconception with regard to the duration of the embryonal life, and gave a quotation frem the text- 

 book by Korschelt and Heider. I have here tried by demonstration on my figures to maintain 

 more in detail that all Pycnogonida pass through the same series of larval stages, whether the larva 

 Protonymphon frees itself at once, or remains in the egg till all the ambulatory legs are developed, 

 even if it has not attained its full length, segmentation, or all its appendages. 



When the yolk-division is equal the whole blastoderm, only excepting the 

 middle and hinder parts of the dorsal side, participates in the formation of the em- 

 bryonal limbs and the proboscis. The embryo is free at once, is considered to be a 

 fully developed larva in the first stage, and is called Protonymphon (Hoek) or Pan- 

 topod-larva kat' exochen (Dohrn, Morgan). 



It is the enormous, overruling development of the embryonal limbs and the proboscis that is 

 a characteristic feature of this larval form, and this feature is found spread through the whole system 

 of the Pycnogonida, and has been known and described in different genera, as Phoxichilidium, Pycno- 

 gonum, Phoxichilus, Ammothea (Achclia), Ascorhynchiis, and Tanystyhitii. It is also this larval form 

 which has originally played the greatest part as to the question of the systematic position of the 



