50 EDGAR J. ALLEN. 
under consideration frequently stain in the abdomen, when 
the longitudinal fibres commence to take up the methylene 
blue at a wound made at the level of the esophagus, from 
considerations of a similar nature to those already adduced in 
the case of the abdominal elements B (4), leaves little doubt 
that the fibres actually go to the brain. The observations 
now recorded, although they do not directly demonstrate the 
point, render it still more probable. 
With regard to the second branch given off by these ele- 
ments after entering a ganglion, which is directed backwards 
along the ganglionic cord, no definite termination has been 
found. It has never been seen to pass through more than 
three ganglia, and can generally only be followed through two. 
This, however, is probably due to incomplete staining, and the 
entire course of this branch remains yet to be determined. 
EXPLANATION OF PLATE 4. 
Illustrating Mr. Edgar J. Allen’s “ Studies on the Nervous 
System of Crustacea.” 
Fic. 1.—Brain and thoracic ganglia of Homarus embryo. es, (so- 
phagus. ¢r.dr. Transverse bridge behind cesophagus. com. Csophageal 
commissure. azt.11. Ganglion of Antennaul. Th.1—1x. Thoracic gan- 
glia. For individual elements see text. Somewhat diagrammatic. 
Fic. 2.—Three abdominal ganglia of Homarus embryo. Motor elements 
inserted upon both sides. For individual elements see text. Somewhat 
diagrammatic. 
Fic. 3.—Ditto. Motor elements inserted upon one side only. 
Fics. 4 and 5.—System of nerve elements in Th. m1 and Th. Iv of Ho- 
marus embryo. 
Fic. 6.—Abdominal ganglion of Homarus embryo. B (4). Element 
sending fibre to brain. 
Fie. 7.—Sixth abdominal ganglion of Homarus embryo. B (4) and 
B (c). Two elements sending fibres to brain. 
Fic. 8.—Second and third abdominal ganglia of Homarus embryo. 
Camera drawing from preparation preserved in ammonium picrate. a. 0. 
motor elements. 
