SCHIZOPODA. 



135 



Assuming that the foregoing observations are correct, the most 

 striking feature in the development of Mysis, apart from the absence 

 of the gastrula-invagination,* is the relation of the entoderm to the 

 food-yolk. The rudiment of the entoderm here remains in close 

 connection with the germ-band (Figs. 65, en, I, and 66, I), and does 

 not enter into any closer relations to the food-yolk, except at the 

 close of development, when it grows round the yolk to form 



ms 



Fig. 65.— Longitudinal section (some- 

 what lateral) through the Nauplitis 

 stage (c/. Fig. 77 C) of Mysis (after 

 Nusbaum) a', first antenna ; a", 

 second antenna ; d, food-yolk ; ec, 

 ectoderm ; en, entoderm ; k, germ- 

 band ; I, rudiment of the liver ; 

 md, mandible ; og, rudiment of the 

 optic ganglion. 



Fig. 66.— Transverse section through a somewhat 

 older stage of Mysis (after Nusbaum). d, food- 

 yolk ; ec, ectoderm ; g, rudiment of the ventral 

 ganglia ; I, hepatic rudiments ; ma, mesoderm. 



the mesenteron. The disintegration of 

 the food-yolk is here not achieved by 

 the actual entoderm-cells, but by the 

 vitellophags above mentioned. We are none the less led by a 

 comparison with Astacus and Palaemon to see, in both these 

 elements, constituent parts of the entoderm. Even in Astacus, it 

 was evident that the cells of the ventral wall of the entoderm- 

 vesicle took little part in the assimilation of the food-yolk. From 

 this region, especially from the point lying immediately upon the 



* According to Wagner, of whose treatises only the second has come into 

 our hands, the gastrula-invagination appears, in Mysis, to be represented by 

 an ingrowth of cells in which, later, a fissure-like cavity appears (No. 40). 



