Manchester Memoirs, Vol. xlviii. (1903), No. 4 



IV. Suggestions for a Revision of the Classification 

 of the Polyclad Turbellaria. 



By F. R Laidlaw, B.A. (Cantab.) 



Received Nove?nber 20th. Read December ist, igoj. 



I. Introduction. 



In dealing with the various genera and species of the 

 Acotylean Polyclads which I have been able to examine, 

 I have in most cases given more attention to the structure 

 of the terminal parts of the genital ducts than to that of 

 the other organs of the body, because I believe that they 

 afford the readiest means by which any species may be 

 referred to its proper genus, and at the same time they 

 give a safe indication of the affinities of the various 

 genera. 



An examination of these organs in a considerable 

 number of genera shows that there is much less variation 

 in the plan on which the vagina is constructed than in the 

 case of the male organs. In fact, the vagina of almost 

 any Polyclad may be referred to one or other of two 

 types ; the only exception that I am acquainted with 

 being found in the case of the specialized genus Parapla- 

 nocera}-. Leaving the consideration of this genus for the 

 present, and confining our attention to the two ' normal ' 

 types, we may take as the first that in which the vagina 

 ends directly, at its proximal end, in the two large egg- 

 ducts which will be spoken of as the uteri. 



The vagina of this first type^ is a perfectly 

 simple duct, which often widens near its outer end, at the 

 point where the shell-glands pass their secretion into it. 

 This is the condition found in the Cotylea. In those 



^See Note A. 

 ^See Fig. i, p. 7. 



December 30th, IQOJ. 



