Explanation of the plates. 
Plate 1. 
The illustrations are drawn under the camera lucida, from the 
microscope directly upon the stone. The preparations (exept fig. 5 & 6) 
were fixed i chromo-aceto-osmic acid and stained with hæmatoxylin. 
Fig. I. Homarus vulgaris. (Magnified 60 diameters ; Zeiss AA, 2.) 
Transverse sections of an oesophageal commissure. a Ex- 
ternal sheath. h Layer of connective tissue inside the 
ext. sheath. c Inner layer or sheath of connective-tissue 
closely applied to the contents of nerve-tubes (compare 
fig. $, a), t, t\ ti Large nerve-tubes with more or less 
concentrated axes. t^^ Large nerve-tubes with no axis. 
nt Central bundle of largish nerve-tubes. s nt Masses of 
small nerve-tubes, more peripherically situated. 
» 2. Homarus vulgaris. (Magnified 950 diameters; Zeiss. Hom. 
im. 7i8^ A P^^t of fig. I, representing some smallish 
nerve-tubes of various sizes, more highly magnified. The 
transsected primitive tubes, of which the contents of the 
nerve-tubes are composed, are distinctly visible as round 
meshes. i, t Largish nerve-tubes in which a concentration to- 
wards an axis is visible. t\ £ Small nerve-tubes ; in one of them 
a slight concentration towards an axis is visible. Small 
nerve-tube in which no concentration towards an axis is 
visible, a Vacuoles. 5 Neuroglia-substance. c The sheath 
of a large nerve-tube which is illustrated in fig. i, 
å Vacuoles in some nerve-tubes, probably artificially pro- 
duced. h Neuroglia-nuclei. 
» 3. Homarus vulgaris. (Magnified 950 diameters; Zeiss. Hom. 
im. \,\8' Transverse section of a large nerve-tube 
with axis (it is the same tube which is illustrated in 
fig. I, t^). a Neuroglia-sheath. 1) Sheath of another large 
nerve-tube. 
