472 AUSTRALIAN HIRUDINEA, III., 



The genital ducts call for no special remarks. The genital 

 apertures are separated by a single annulus. The male pore lies 

 between annuli 27, 28 (20th and 21st postoral annuli), and the 

 female pore between 28, 29 (21st and 22nd postoral annuli). 

 From an examination of fig. 8, showing the metameric constitu- 

 tion of the animal, it will be seen that the male pore lies between 

 the 1st and 2nd, the female pore between the 2nd and 3rd annuli 

 of somite xii. In this connection I would remark that it would 

 be preferable if all workers at the group stated the position of 

 the genital apertures definitely in terms of the postoral annuli, 

 inasmuch as their exact position is an important point; and, it 

 seems to me, many mistakes are liable to creep in, in stating 

 their position in terms of the anterior annuli in an absolute way. 

 The position of the genital pores in somite xii., agrees in detail 

 with that in G. stagnalis, G. fusca, and G. elongata; and that of 

 the male pore alone with the similar aperture in G. heterodita. 



In connection with the position of the genital apertures, lies 

 something of phylogenetic interest, particularly so as one can, I 

 think, make out the primitive condition with some accuracy in 

 regard to the genital apertures. Taking, firstly, into considera- 

 tion the commoner European and North American species, one 

 finds the arrangement of the apertures to be as follows : — 



G. complanata... \ \ apertures 



O. coneolor ( J^ between annuli o somites xi,, xii. (separated 



G. parasitica .... f 2 between annuli 2 and 3, somite xii. | by two 



G. elegans ) ) annuli. 



G.. heterodita.... ^ $ united, between annuli 1 and 2, somite xii. 



G, stagnalis \ \ apertures 



G. fusca f (^ between annuli 1 and 2, somite xii. (separated 



G. elongata f $ between annuli 2 and 3, somite xii. [by one 



G. Intermedia... ' ) annulus. 



From the central position occupied by G. heterodita, with 

 regard to the other species, not onh'' in connection with the 

 genital apertures, but also numerous other characters; and 

 taking into consideration the fact that the positions of the 

 apertures in the three groups given above, into which the species 

 fall, one may conclude that the genital apertures are in their 



