40 
genus the distance between the female and male genital pores is 
small. Pars externa vaginae is nearly perpendicular, but the shell 
giand duet ootype runs over the antrum masculinum and reaches 
rostrally the level of the caudal end of the prostate giand. It is 
particularly interesting to note this location, as a peculiar condition 
exists in two S^y/oc/i/d-genera, Idioplanoides and Limnostylochus, 
where the shell giand duet has been moved so far forward that it 
lies rostrally to the prostate giand. Thus we have in this new genus 
an obvious tendency in the shell giand duet to move forward. The 
influence brought upon the middle intestine by the copulatory 
apparatus, male as well as female, through their unusual develop- 
ment and location immediately back of the pharynx has already 
been mentioned. It is obvious that on account of the considerable 
size of the prostate vesicle in the Stylochids a better development 
of the shell giand duet would mean a removal of it from this 
vesicle. In the two Stylochid-genera mentioned above this has 
been possible, while keeping the genital pores close to each other, 
simply through an enormous extension of the pars externa vaginae, 
devoid of shell giands, giving the part of the vagina that forms 
the loop (i. e. the shell giand duet) a chance to develop fully in 
front of the male copulatory organ. Thus the change is dependent 
on the faet that sufficient space is lacking through the inerease in 
size of the prostate vesicle. 
I must here add a few words regarding Idioplana, as it is not 
improbable that the same condition exists in this Polyclad in regard 
to the shell giand duet as in Idioplanoides and Limnostylochus. Wood- 
worth (1898), its only observer, gives no information as to where 
the shell giands empty. If his description is absolutely accurate, 
the shell giand duet must lie above the prostate giand. His de¬ 
scription is as follows: „The female gonopore leads into a spacious 
bursa, from which the vagina, with diminishing calibre, leads up- 
ward and backward over the male organ, and receives the oviducts 
which open into it opposite to one another at a point above the 
posterior limits of the penis. The canal, which is ciliated throughout, 
and which from now on is reduced in diameter and uniform in 
calibre, passes forwards and downwards over the penis, reaching 
nearly to the ventral wall, and then bends upwards and backwards 
again, passing over the vagina and terminating a little posterior to 
thj female gonopore in a vesicle or enlargement, „accessorische 
