﻿PYCNOGONIDA. jr 



large and small >olk parts, the macromeres and raicromeres of Morgan, must be of a considerable 

 influence for the later development, and that it is connected witli or proportioned to the mass of the 

 alimentary yolk in the egg; this fact again pla}s a ver}- great part in the biology of the larva, as 

 this latter may exist without any other food, and keep enclosed in the safe egg-shell the longer, the 

 more alimentar\- yolk it brings along with it. Kroyer already has referred to this reciprocal relation 

 in his Contributions to the knowledge of the Pycnogonida ■ (1845), conip. especialh' the third of tlie 

 five principal heads, under which he collects the results of his examinations, 1. c. p. 137, and to which 

 I have referred at p. 12 secj. 



A germinal stripe as in the other Arthropoda, especially the Insecta, is not 

 formed. The ganglia as well as the separate pairs of limbs are formed or constricted 

 b\' degrees, from before backward, and, with the exception of the three foremost 

 ganglia and pairs of limbs, one after the other. 



In the Arthropoda, especialh- the Insecta, the first germ of the einbr\-o, as is well known, is 

 distinctly seen as a smaller or broader longitudinal band, the germinal stripe, along the under side 

 of the egg, and from this band the formation of the abdominal nerve cord and the pairs of limbs take 

 their rise almost at the same time; besides the formations are onh- small, and, as far as thev really 

 are developed, they grow in size and length by a rapid multiplying, proliferation, of the cells. In 

 the Pycnogonida, on the contrary, a germinal stripe is never found, but the whole yolk mass is 

 innnediately enclosed b)' a blastoderm, and all the limbs arise, if an\-thing, from the sides of the bla- 

 stoderm by a segmentation of corresponding parts of the blastoderm with enclosed yolk mass. Further- 

 more only the three first pairs of limbs, the embryonal legs, are formed at the same time, while the 

 following four pairs, the ambulator)' legs, are segmented off by degrees from before backward, most 

 frequenth- one pair after the other and with longer or shorter intervals of time. The ganglia seem 

 to develop contemporaneously with the embr\-onal limbs, and the ganglia of the abdominal side are 

 divided into two principal sections, a foremost one for the embr\'onal legs, and a hindmost one for 

 the ambulatory legs; but this latter mass of ganglia is not till a later stage sejDarated into four or 

 five pairs of ganglia by degrees as the ambulatory legs develop. I may refer to m\- figures pi. I, 

 fig. II and pi. II, fig- 18, both representing what I call the second larval stage; the first figure repres- 

 ents PsciidnpaUcuc circularis, in which the whole mass of ganglia is seen still undivided, and only the 

 nerve mass belonging to the segments of the embryonal legs, has been slightly separated; the other 

 figure represents NyiiipIiPii Sliiitcri , in which the two pairs of ganglionic centra ma\- be distinctly 

 discerned imited to a common mass, while the nerve mass of the first pair of ambulatory legs is well 

 separated from the following mass representing the ganglionic mass of the three following pairs of 

 ambulatory legs, in which mass, however, as yet only two pairs of ganghonic centra are to be seen. 

 The larva of Xyinphoii Sluitcri upon the whole is more developed than that of Pstudopallcni: 



Between the embr\-oual and the larval stage tlierc is uo distinct boundary, in 

 so far as this boundary is to be determined by the embryo's leaving the egg; but the 

 enibr}-o leaves the egg sometimes on an earlier, sometimes on a later stage. 



I have already before mentioned that according to the common \ie\v the limit of the embryo- 

 nal stage is formed by the embryo breaking the egg shell or egg membrane, and that the whole 



