GEROULD: CAUDINA. 179 
12 y, the large oval nucleus measuring 4 a X 6 a. The nuclei show 
indications of a chromatic network with minute chromatic bodies 
situated near the periphery of the nucleus and at the points of junction 
of the threads. Each of these cells probably divides twice, as shown 
by Field (93) in other echinoderms. 
The smaller cells (Fig. 106), which are to be regarded as sperma- 
tocytes (sp'cy.), have a spherical nucleus and very little cytoplasm. 
The nucleus has in sections a diameter of about 4 a. Under certain 
conditions the nuclei of these cells stain diffusely, whereas in the 
nuclei of spermatogonia from the same tubule only the nuclear mem- 
brane, the network of nucleoplasm, and the chromatic bodies are 
stained. 
The still smaller cells in the same tubule, which are to be regarded 
as spermatids (sp'd.), also stain diffusely (in Czokor's cochineal). 
The mature spermatozoón is about 60 % in length; its head (exam- 
ined in a fresh condition in sea-water) is about 3.6 a in diameter. 
I have not detected signs of karyókinesis in the germ-cells in any 
of the testes which I have examined. The specimens were taken 
from October to February, inclusive. Nor have I found any cell 
division going on in the ovaries, which were taken at short intervals 
between the middle of October and the middle of April. It seems 
highly probable, therefore, that the summer months are the period 
during which the germinative epithelium of both testes and ovaries 
is in a state of active cell division. 
The spermatozoa are mature during the months of February, 
March, and April, and perhaps for a longer time. During these 
months I have several times observed the emission of sperm by 
specimens which I was keeping alive in an aquarium. The females, 
which I was able to keep three or four weeks at a time during the 
winter and early spring, unfortunately never laid eggs while in cap- 
tivity, nor have I succeeded in fertilizing artificially ova taken from 
the ovaries. 
Genital duct. The wall of the genital duct (Plate 8, fig. 105) 
consists of (a) an external layer of epithelium composed of flat, 
ciliated cells, (5) a thick layer of fibrous connective tissue, (c) longi- 
tudinal muscle fibers, which lie in the midst of the connective-tissue 
layer, and (d) an internal epithelium consisting of columnar or 
spindle-shaped collared cells. 
In the proximal extremities of the genital tubules, J. e, in the 
region where eaeh unites with the genital duct (Plate 8, fig. 103), 
