STUDIES ON THE NERVOUS SYSTEM OF CRUSTACEA. 497 
microscope these threads will be seen to be beaded, and gene- 
rally show all the various forms assumed by nerve-fibres. 
EXPLANATION OF PLATES 37 and 38, 
Illustrating Mr. Edgar J. Allen’s paper on “Studies on the 
Nervous System of Crustacea.” 
Fig. 1.—Diagrammatic view of the connections of the stomatogastric 
system of Astacus with the central nervous system. Br. Brain. com. (so- 
phageal commissure. com. gang. Commissural ganglion. ¢r. dr. Transverse 
bridge behind cesophagus. «@s. gang. (isophageal ganglion. azy. Azygos 
nerve. ant. med.n. Anterior median nerve. dors. 2. Dorsal nerve. vevt. n. 
Ventral nerve. aand 4. Branches of ventral nerve. c. Median nerve from 
cesophageal ganglion. dande. Branches of ventral nerve. mew. Neuropile. 
C,, C,. Bipolar ganglion cells. D. Unipolar ditto. H. Fibre connecting 
brain with commissural ganglia. . Motor nerve-ending. J and Z. Sensory 
nerve-cells. WV. Fibre connecting gastric ganglion with commissural ganglia. 
O. Fibre connecting commissural ganglia. 
Fie. 2.—Ditto, of lobster embryo. Lettering same as Fig. 1. 4 and B. 
Cells of commissural ganglia. /. Cell of cesophageal ganglion. gast. gang. 
Gastric ganglion. m.z. Nerve from commissural ganglion to region round 
mouth. 
Fie. 3.—(sophageal ganglion of Astacus. Drawn from one preparation. 
Lettering as in Fig. 1. 
Fic. 4.—Lower portion of cesophageal ganglion of Astacus, enlarged. 
Drawn from one preparation. As in Fig. 1. 
Fie. 5.—Ganglion cell from gastric ganglion of adult Astacus, showing 
connective-tissue sheath with its nuclei. JV. Nucleus of cell. 2. Nuclei of 
sheath. Cell process stained with methylene blue; cell itself only slightly 
stained. xX 420. 
Fic. 6.—Ganglion cell of gastric ganglion of adult Astacus, showing 
branches to neuropile. Methylene blue, fixed with ammonium picrate. 
Camera drawing. X 250. 
Fic. 7.—Ditto, showing two main fibres (I and II). Methylene blue, fixed 
with ammonium picrate. Camera drawing. X 250. 
