SOME POINTS IN DEVELOPMENT OF SOOEPIO EULVIPES. 593 



of the epiblast where the ganglia will be formed, there is uo 

 trace of the nervous system in the body. In the cephalic 

 region the brain is beginning to form as in Euscorpius by 

 the proliferation of the cells of a pair of cerebro-optic in- 

 vaginations, which are more lateral in position than in the latter 

 species, but otherwise completely correspond to them. 



At a considerably later stage the gut begins to be constricted 

 by both circular and longitudinal bands of mesoblast (fig. 13), 

 which divide it into a central tubular portion with a series of 

 large diverticula which form the so-called liver. Both the gut 

 and the liver remain full of granular matter, from which the 

 body-cavity is quite free. The ventral nervous system is 

 by this time completely separated from the epiblast, but as its 

 formation presents no special points of interest I have not de- 

 scribed it in detail. In the head the stomodseum becomes very 

 chitiuous, and is furnished with powerful lateral muscles (fig. 

 14, m). Just opposite the aperture of the stomodseum is the 

 lower end of the cord of cells which forms the coiled appendix 

 described above (p. 589), and it is by the destruction of this cord 

 of cells that the embryo nourishes itself through all the later 

 stages of embryonic life. This mode of nutrition, which was 

 imperfectly described by Duveruoy,^ is very exceptional, and, 

 indeed, more like the nutrition of a young marsupial than any- 

 thing else. The cord is held in position by the chelicerae 

 (fig. 14, 1), and this is the object of the phenomenally early de- 

 velopment of these appendages as well as of the storaodseum. 

 The comparatively early formation of the gut is due to the 

 same cause. As might be expected, the chelicerse are con- 

 siderably modified to serve their peculiar function. This is 

 best seen in the oldest stage in ray possession (figs. 15 — 17), 

 where the chelicerae, apart from their great proportional size, 

 are seen to have the third joint specially developed (fig. 17, 1, 3). 

 This third joint is very much larger than the other half of the 

 pincer, and is further provided with a strong band of chitin 

 ■which runs in a somewhat sinuous manner from the base of 

 the joint up to the tip. This band of chitin is grooved, and the 



^ Loc. cit. 

 VOL. XXXII, PAKT IV. — NEW SEE. R K 



