244 BUMPUS. [Vol. V. 



seems to occur between them and the second antennae. An 

 elevated ridge represents the connective joining the ganglia of 

 the antennas and second antennae. 



The second antennae now show a marked tendency towards 

 segmentation and division. Very soon they will become bi- 

 ramous. Their ganglia are clearly connected with the ganglia 

 of the jaws by a continuation of the elevated connectives 

 already noted. This elevation may be continued even to the 

 thoracico-abdominal plate, which has now lost its earlier eleva- 

 tion, and has become quite flush with the surface of the egg in 

 certain preparations. This depression of the tract is quite dif- 

 ferent from the condition of Astacus. 



A median longitudinal section (Fig. 8) has a relatively even 

 contour, the inpushing of the mouth being the most consider- 

 able break. The ectoderm is still made up of a single layer of 

 cells, though in places — for example, under the upper lip — a 

 thickening is seen. In the neighborhood of the now closed 

 blastopore the ectoderm is considerably thicker. Mesoderm is 

 not much more abundant than in the previous stage, though 

 the number of chromatin grains is truly surprising. A thick 

 layer extends from the anterior portion of the procephalic lobes 

 to the deeply projecting entodermal mass, thinning out only in 

 the neighborhood of the stomodaeum. The grains are often of 

 considerable size, and seem to float in a serum. The entoderm 

 shows little change, though in certain central portions bands of 

 clear protoplasm are to be seen. These bands are arranged 

 longitudinally with the entodermal mass, and are bordered by 

 closely associated nuclei. In a few instances the yolk enclosed 

 by the peripheral entodermal cells seems to show a tendency 

 towards the formation of entodermal yolk pyramids, as de- 

 scribed for Astacus. The proctodaeum has not yet reached pro- 

 portions that make it a prominent object. 



Fig. 4 represents a transverse section through the procephalic 

 lobes, the thickenings for the compound eye being shown at Ce. 

 The absence of mesodermal cells from the median portion and 

 the median mass of chromatin grains may be noted. 



The section passing through the mouth (Fig. 5) shows the 

 invagination of the ectoderm, and also demonstrates the ganglia 

 of the first antennae (G. 3 ) as thickening tracts of ectoderm. The 

 section through the antennae shows that they are being actually 



