29 
static secretion are later emptied to the outside; the vigorous 
sperma has then already made its way through the median uterine 
duet into the uteri, where the spermatozoa fertilize the eggs. Ac- 
cording to such an interpretation, the organization of Trigonoporus 
should hypothetically represent an earlier stage in the change of 
the duet of Lang’s glandular vesiele. The duetus vaginalis is not 
yet adapted for the aet of eopulation, a funetion that it probably 
has in the other eases. 
Gonclusion. 
In regard to the systematie position of Ceratoplana, it has already 
been pointed out that there is a marked relationship to the genus 
Stylochoplana. Detailed explanation seems unneeessary, as doubts 
ean seareely arise after the above deseription. The diseussion of 
the duetus vaginalis also shows that this feature, the most eharae- 
teristie of Ceratoplana, ean be traeed direetly baek to the organi¬ 
zation of Stylochoplana. The idea of the duetus vaginalis as ori- 
ginating from the duet of Lang’s glandular vesiele has here, for 
the first time, been given a detailed and full explanation. This 
analysis also gives an aeeeptable explanation of the faet that the 
duetus vaginalis may oeeur here or there in various Aeotylean 
families. This assumption is based on the faet that Lang’s glan¬ 
dular vesiele belongs to the organization-plan of sueh families where 
a duetus vaginalis oeeurs. The diseussion also verifies my state¬ 
ment of 1913, that the organization of the female apparatus is of 
little value in the elassifieation of Åcotylea into families. Anything 
else is hardly to be expeeted, when one may find sueh an extra- 
ordinary agreement in the female apparatus as exists between that 
of eertain Trielads (for instanee, Procerodes-s>pQO\Qs) and that of 
Polyelads {Stylochoplana, to use only one example). In speeies of 
Procerodes we reeognize the „Eiergang“ as the median uterine duet 
of Polyelads, and the vagina of Polyelads in the part lying distally 
to the orifiee of this duet (this part is named „Drusengang“ by 
Bohmig, „Vaginaloviduet“ by Wilhelmi). The vagina of the Trielads 
eontinues proximally in the duet leading to the „uterus". This 
„Uterus" and „Uterusstiel" (v. Graff in Bronn) or „Reeeptaeulum" 
and „Vaginalstiel" (Wilhelmi) I regard as homologous to Lang’s 
glandular vesiele and its duet (see Boek, 1923 b). 
