No. 2.] EMBRYOLOGY OF THE AMERICAN LOBSTER. 247 



of nuclei, as shown in the drawing. Within, the hind-gut passes 

 into the mass of diffused entodermal cells, which are now trav- 

 ersing the yolk, but keeping, in a rough way, a definite order, all 

 tending towards the periphery. The true mesoderm cells (Ales.) 

 surround the proximal portion of the hind-gut. Chromatin ele- 

 ments are less abundant than in the immediately preceding 

 stage. 



A section parallel to 13 (Fig. 12), drawn through Fig. 1 at 

 12, shows at G. 2 the invagination at the base of the optic tract, 

 the cerebral lobe or ganglion. Just behind it lie the ganglia of 

 the antennae (G. 3 ) and second antennas (G. 4 ). A section through 

 the jaw, which contains mesodermal elements in its lumen, is 

 also shown at J. At several places in these sections the meso- 

 dermal nuclei seem to be breaking down into chromatin gran- 

 ules. I am still in doubt, however, whether such is the case. 



A transverse section (Fig. 4) through 4 of Fig. 1 passes 

 through the procephalic depressions. One or two mesodermal 

 cells are to be noted, as well as collections of chromatin grains. 

 Fig. 5 is drawn through the ganglionic region noted in Fig. 12 

 at G? An appearance of invagination is given, which is even 

 more clearly shown when we examine sections of the remain- 

 ing pairs of ganglia. Beneath the ectoderm mesodermal cells 

 are seen and chromatin grains are present, exhibiting, in the 

 main, general symmetry, though isolated nebulae may be ob- 

 served at varying points. The median elevation, below which 

 several mesodermal cells are shown, is the ridge which passes 

 anteriorly from the upper lip. 



Section No. 6 passes through the anterior portion of the fore- 

 gut, as well as through the first pair of appendages. The posi- 

 tion of the fore-gut is slightly eccentric, while the cavities of 

 the appendages appear to contain yolk grains surrounded by 

 chromatin granules. The mesodermal cells which fill in the 

 body of the upper lip are still associated with yolk grains. 

 Many of the cells have pseudopodial prolongations. The next 

 section (Fig. 7) passes directly through the ganglionic swellings 

 at the base of the first pair of antennae. The arrows indicate 

 the direction of invagination. Chromatin granules are abun- 

 dant near the yolk. Six sections back, the knife passes through 

 the free tips of the first pair of antennae (Fig. 8), and through 

 the body of the second pair, the internal boundaries of which 



