165 
Mortensen’s, also in other respects, very valuable collection of 
Turbellarians. 
Before leaving Enterogonia, I may point out that the prostatic 
vesicle has evidently been removed from the penis and obtained 
a horizontal location similar to that in Stylochus, before the reduc- 
tion of it to a mere appendix of scarcely any functional value 
took place. 
As I pointed out in 1913, Meixneria, collected by Dr. Morten¬ 
sen in Siam, is a rather primitive Stylochid. The male apparatus 
has a prostatic vesicle situated close to the penis, and the latter 
being small, the condition conforms more closely to what I have 
above regarded as the original feature of the male apparatus than 
the case is in any other Stylochid .except perhaps Idioplana. The 
penis is not very far from being only the apex of the vesicle. 
Provided only with a feeble muscularis, the narrow ductus ejacu- 
latorius opens near the tip of the penis into the efferent part of 
the prostatic vesicle. The existence of false seminal vesicles, as 
well as a fold (= penis-sheath) projecting into the antrum, are 
secondary features. The prostatic vesicle, although very developed, 
has not reached the complication in the form of tubules met with 
in the genus Stylochus. The intracapsular glandular layer is thick 
and compact without separating septa, and has an undulating con- 
tour. On a close inspection it seems possible to distinguish between 
low epithelial cells and a heavy sub-epithelial layer filled up with 
granular secretion, as I have described for Discostylochus. 
This differentiation inside the muscular envelope is absent in 
the prostatic vesicle of Cryptophallus and Par asty lochus, where the 
epithelial giand cells are immediately surrounded by the muscu¬ 
laris. As the epithelium contains the giand cells, it reaches a fair 
thickness. The inconsiderable size of the vesicle in these two genera 
I regard as a regressive feature. The location of it in the penis 
could perhaps be regarded as primitive, but the stoutness of the 
penis and the reduction of the vesicle which has taken place allow 
no safe conclusion in this respect. That giand cells are included 
in the epithelium of the vesicle conforms also to a primitive con¬ 
dition. The weak and loose muscular envelope and the diminished 
number of extracapsular giand cells are features, agreeing with my 
view that a reduction has actually occurred. Only in these two 
