1 82 BULLETIN OP THE BUREAU OF FISHERIES. 



EMBRYONIC DEVELOPMENT. 



Segmentation. — Because the eggs are not regularly arranged in the external sacks 

 there is a corresponding irregularity in the position of the embryos. In consequence 

 of lack of material it has not been possible to follow the various cleavage stages as 

 fully as in the Lernaeopodidse." But the few stages that have been obtained corre- 

 sponded exactly with those found in the Lernaeopods, and there is thus a strong prob- 

 ability that the other stages also correspond. At all events it is safe to say that cleavage 

 in this genus resembles that in Achtheres, Clavella, and Brachiella far more than it does 

 in Lern<20cera {Lermza) as given by Pedaschenko (1898). 



Blastula. — The blastula shown in figure 20 is practically identical with that of 

 Achtheres,'' the only difference being an increased thickness of the blastoderm disk. 



The yolk here shows that all of the cytoplasmic material has migrated to the surface 

 and entered into the blastoderm. Now, also, there are good-sized vacuoles in the yolk, 

 possibly as a result of this withdrawal of material. There is no evidence in any of the 

 sections of the formation of a blastodermic cuticle similar to that secreted by the 

 Achtheres embryo. Further material may reveal the presence of such a cuticle, but its 

 absence seems fully as much in accordance with the subsequent development of the 

 present genus. For we do not have here a shifting back into embryonic life within the 

 egg of the early stages of development, such as occurs in Achtheres. 



In that genus all of the nauplius and metanauplius stages are passed within the 

 egg, and the lar\-a hatches either in the last metanauplius stage and molts within an 

 hour into the first copepodid stage or hatches directly into the latter stage. Here, on 

 the contrary, the larva hatches into an ordinary nauplius and none of the early stages 

 are passed inside the egg. 



THE NEWLY HATCHED L.\RVA. 



Nordmann, Briihl, and Hartmann have given us figures of a newly hatched larva 

 (fig. 22, pi. ix), but Briihl's figure was simply a copy of Nordmann's, and Briihl himself 

 had never seen a larva. Of the other two figures, Nordmann's is by far the better and is 

 accompanied by an excellent description. Hartmann showed a series of eggs taken 

 from the egg sack in various stages of development and also a "free larva." But he 

 gave no description, and the larva which he designated as "free" had four pairs of 

 appendages instead of the three shown on another larva just emerging from the Qgg 

 membranes. The former, therefore, probably represented a lar\^a that had had at least 

 one molt, and hence was not newly hatched. 



Nordmann stated that he actually witnessed the emergence of the lar\ra, inclosed 

 in its two membranes, from the egg sack, the bursting of the outer membrane, and the 

 swelling and rupture of the inner membrane. 



Since his figures of the corresponding larvae of the genus Achtheres were wonderfully 

 correct, we can accept these of Lerrucoccra on the same basis. According to his account 

 the larva was a nauplius with the usual three pairs of appendages. The body was 

 oval or ellipsoidal, with its lateral margins tolerablj- parallel, and about 0.25 mm. long. 



It was covered on both the dorsal and ventral surfaces by a delicate shield or 

 carapace, of a greenish color in that particular species (esocina), well arched dorsally, 



o Proc. U. S. Nat. Mus., vol. 39, p. 196. *• Proc. U. S. Nat. Mus., vol. 39. pi. 39, fig. 8. 



