1 882.] Some of its Developmental Stages. II 



pigment masses, the latter being nearer the dorsal line. It must 

 be understood that the embryo in Isopod crustaceans is bent 

 backward, head and tail nearly touching each other, the limbs, on 

 the other hand, being in the peripheric layer. In Fig. 4 an em- 

 bryo is shown freed from the egg-skin or chorion,. thereby turned 

 into its opposite direction, concave ventral and convex dorsal 

 side. A pereiopod or thoracic leg ; the end of the abdomen (tel- 

 son) with the last pair of legs (uropods), a pleopod, one of the 

 second pair of antennae with dd— ? remnants of earlier embryonic 

 bristles — are shown respectively in Figs. 4, 4a, 4 b, 4c, and ^d. 

 By working with the dissecting needles, the embryo (in Fig. 4 

 freed from the chorion, but still enclosed in its larval skin) with 

 some difficulty could also be freed, limb after limb, from its lar- 

 val skin (amnion), then appearing as in the much enlarged Fig. 5. 

 This, as has already been said, is the highest and most advanced 

 stage of the Bopyrus, which, under favorable circumstances, will en- 

 ter the gill-cavity of the earlier developmental stages of the prawn, 

 where it, as the prawn advances, will, when a female, lose its eyes, 

 both antennas, the uropods, etc. ; while the pleopods will deform 

 into the abdominal lobes and from the seventh free segment will 

 bud a pair of legs. But if a male, where does the eighth pair of 

 thoracic legs originate from? From the first pair of pleopods ? I 

 should rather infer that the pair of uropods will yield the eighth 

 pair of legs in the male. The fact that the male has no abdominal 

 appendages (so-called gills of the female) gives strength to the 

 assumption that the eighth pair of legs in the male are derived 

 from one pair of the pleopods, since the former (female) have 

 the same origin. 



EXPLANATION OF PLATE I. 

 Flu. 1.— Egg after segmentation. 

 a. Blastoderm-cells. 



