PLANARIANS FROM MAURITIUS AND RODRIGUES 1538 
ventral, surface. Such an opening dorsally situated is also 
known to occur in Acoelean forms, suchas Cylindrostoma 
quadrioculatum Jens, and C. klostermanni Jens. 
The discovery of Laidlawia (15) mentioned above may 
be regarded as of some importance, as it may constitute an 
additional link in the chain of evidence against the homology 
of the part of the duct, as has been suggested by Lang (18). He, 
in his monograph, has the following passage : ‘ In morphologi- 
scher Beziehung erinnert der Canal, insofern er eine Verbindung 
zwischen der Hinmiindungsstelle des Uterus in den Kiergang 
einerseits und der Aussenwelt anderseits darstellt, einigermassen 
an den Laurerschen Canal der Trematoden und Cestoden.’ 
A comparison with the Laurer’s canal of the Malacocotylean 
Trematodes, which passes up from the oviduct, in the neigh- 
bourhood of the ootype, and opens by a minute pore on the 
dorsal surface, obviously suggests itself. 
Great interest is attached to the existence of some Polyclads 
having the dorsal passage of the vagina, which opens either to 
the exterior on the surface of the body, or into one of the intes- 
tinal coeca, as stated above. The homology between the genito- 
intestinal canal of the Heterocotylea, the Laurer’s canal of 
the Malacocotylea, and the duct leading to the receptacle in 
the Aspidocotylea, though it may be open to question, seems 
to have the balance of evidence in its favour. Haswell (14) has 
put forward the view that there can be regarded as representing 
Laurer’s canal in the Polyclads not only the genito-intestinal 
canal of Knterogonia, but the seminal receptacle of the 
Acotylea in general and the posterior female passage, which 
opens to the exterior, as has been observed in ‘some forms. 
I am inclined not only to concur with him, but further to 
develop to a certain extent this view even to the Triclads. In 
this communication, however, I have intentionally abstained 
from making any such attempt, leaving the problem to future 
consideration. 
