﻿i6 



PYCNOGONIDA. 



development taking place before this act, is reckoned to the embryonal stage, bnt 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, nntil all the 

 limbs, the ambnlatory legs included, have been developed, it will be imderstood that Korschelt and 

 H eider, L,ehrb. 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 ganze Lar venentwickelnng vollkommen nnter- 

 driickt, das jnnge Thier, welches die Eischale verlasst, bcsitzt bereits alle definitive Extremitaten, 

 wenn anch 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 Phoxichilidinm , welche den 

 Hydroidpolypen verlasst \ In my opinion the peciiliarit}- in Pallene emaciata ^ the species mentioned 

 by Dohrn, is only to be fonnd 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 nnderstood as something general in the genus, bnt 

 only as apecnliarit\- in this species among known forms I infer from the fact that in another Pff/Zrwr- 

 species, Pallene has fa fa ^ I have fonnd all larvae free with only tlnee pairs of developed ambnlatory 

 legs, pi. I, fig. 18 — 19. In the nearly related genus Pseudopallene I have even fonnd the larva free in 

 its first stage with the two foremost pairs of ambnlatory legs not yet qnite 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 Nyiii- 

 phoii, 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 fonn 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 embrj'onal life, and gave a quotation frem the text- 

 book by Korschelt and Heider. I have liere tried b\' demonstration on my figures to maintain 

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

 « Protonymphon ; frees itself at once, or remains in the egg till all the ambnlatory 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, onl>- excepting the 

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

 bryonal limbs and the proboscLs. 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 embr\ onal limbs and the proboscis that is 

 a characteristic feature of this larval fonn, and this feature is fonnd spread through the whole system 

 of the Pycnogonida, and has been know^i and described in different genera, as Phoxichilidiuju., Pycno- 

 gonum^ Phoxichilus ^ Anunothea (Achelia), Ascorhymchus, and Tanystyhivi. It is also this larval form 

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



