86 THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 
(a) The Testes.—The testes are exceedingly numerous, and arranged in a single 
long row down each side of the body, just outside of the longitudinal nerve cord (Figs. 
4 and 13, 7.), the consecutive testes being very close together, but not, at any rate as a 
rule, actually touching. The row commences on each side a short distance in front of the 
ovary, and extends backwards to a point about half way between the pharynx and the 
external genital aperture. Owing to the impossibility of obtaining any one section to 
pass through the whole row of testes it is difficult to count their exact number, but I 
estimate that there must be at least fifty on each side of the body. 
Each testis (Fig. 30) is a simple, pear-shaped sac, about 0.84 mm. in length, 
with the broad end directed towards the ventral and the narrow end towards the 
dorsal surface of the animal. 
The cavity of the testis is med by an epithelium resting upon a very thin 
membrane. At the broad end the epithelium is very thin, composed apparently of a 
single layer of flattened cells, but at the sides and especially at the apex of the sac 
the epithelium gradually increases in thickness, and is seen to be composed of 
numbers of large cells of the form shown in figure 36. These cells have very large, 
deeply staining, highly granular nuclei, and they are the mother cells of the 
spermatozoa. 
In the centre of the testis, and separated from the layer of mother cells always 
by a very distinct interval (which may be in part due to shrinkage, but which 
certainly indicates a well defined separation), lies a compact mass of developing 
spermatozoa of the general form shown in figure 80. This mass is connected with 
the epithelial lining of the testes at the broad (ventral) end by a narrow neck (Fig. 
30, x.) which indicates the point where the developed spermatozoa pass into a branch 
of the vas deferens. Moseley (6) has already insisted upon this separation of the 
testis into two distinct regions in the case of Bipalium, although in that form the 
inner mass of developing spermatozoa appears to be in contact with the layer of 
mother cells all round. He states that the two regions are so well defined that it 
would almost appear as if a thin membrane were reflected back from the point of 
union of the vas deferens with the testicular sac-wall and separated the two regions. 
He could not, however, make sure of the existence of any such membrane. Indeed, 
it seems highly improbable that such a membrane should exist, and I can find no 
trace of it in my preparations. 
Figures 37 to 39 show three stages in the development of the spermatozoa, found 
in the central part of the testis. The interpretation of these appearances is perhaps 
a little doubtful. Figure 37 represents the earliest of the three stages, which I take 
to be equivalent to a spermatosphere in such a form as the earth-worm, and which is 
probably derived directly from a single mother cell (spermatospore) such as is shown 
