248 BUMPUS. [Vol. V. 



latter extend as a chain of nuclei almost down to the yolk. The 

 ganglia (C7. 4 ) appear as two elevations separated from each other 

 by a median depression. Each is seen to have its cells arranged 

 as if in obedience to an invagination following the direction of 

 the arrows. Though chromatin grains are abundant in the 

 median portion, mesodermal cells are found only at the outer 

 margins of the section. In the next following section, not fig- 

 ured, there are no traces of ganglionic invaginations. In Fig. 9, 

 which passes through the ganglia of the "third " pair of appen- 

 dages, the invaginations again occur, as shown by the arrows. 

 The cavity of the second antennae is not different from the cav- 

 ities of the other appendages. Fig. 10 is drawn through the 

 body of the pair of jaws, which seem to be elevated from the 

 general surface by lateral pressure. The single layer of ecto- 

 dermal cells is quite in contrast with the previously described 

 sections through ganglionic areas. The last section figured 

 (Fig. 11) passes through the biramous tips of the second an- 

 tennae, and cuts the proctodaeum longitudinally. The latter 

 ends blindly, and below it are many feeding entodermal cells. 

 Mesodermal cells are grouped in the neighborhood, several 

 extending out under the ectoderm. Chromatin granules are 

 not specially abundant. At Ent. several entodermal cells are 

 seen devouring the volk. 



Stage N. 



This is most characteristically the nauplius stage of the 

 developing lobster. The appendages are tipped with spines. 

 The second pair is not only biramous, but also clearly jointed. 

 The stomodaeum is covered by the upper lip, which extends 

 posteriorly until it almost touches the tip of the anteriorly 

 directed tail. A cuticle, which in the next stage proves to be 

 a true ecdysis, is seen to be lifted from the embryo in the 

 region of the compound eyes. In certain cases a whitish band 

 extends anteriorly, as figured PI. XIV. Sections of this and 

 the following stages have not yet been made. 



Stage O. 



The sloughed cuticle is clearly seen as a delicate line sur- 

 rounding the embryo and its appendages. A pair of pigmented 



