STRUCTURE OF CLINOSTOMUM 193 



great size of the ventral sucker has not been indicated by the 

 behavior of the animal. I have not seen it used at any time. Its 

 histological structure is such that it would seem to be fully func- 

 tional and its great size indicates a function of considerable 

 importance but no activities have been observed in connection 

 with it. 



POSITION OF THE GENITAL PORE 



MacCallum ('99, p. 699) states that ''at about the middle por- 

 tion of the body behind the ventral sucker the genital openings 

 [italics mine] are seen, close together, that of the female apparatus 

 being directly in front of the male." Also on page 703 he says 

 that the female genital opening is located "directly in front of 

 the male genital pore." These statements certainly imply that 

 there are two genital pores, a condition not found elsewhere in 

 trematodes. The statements are however contrary to fact and 

 are not consistent with MacCallum's figs. 3 and 7 where a single 

 genital pore is clearly shown, so that it is difficult to see how they 

 crept into his paper. The exact position of the genital pore was 

 determined for twenty-two individuals, the data for which are 

 shown in table 2. 



The total length and width/ measurements are given and the 

 distance from the anterior end to the genital pore. In order to 

 make direct comparisons possible the position of the pore in per- 

 centage of total length is given in the column on the right. The 

 opening is thus shown to lie posterior to the center of the body in 

 every instance and to vary between 53.7 per cent and 68.3 per 

 cent as extreme limits. A part of this difference may perhaps be 

 attributable to individual differences of contraction or reagent 

 action but in addition to these we must attribute it in part to 

 variation in the actual position of the pore. If we take the aver- 

 age of these figures we should have 56 per cent as the point of 

 location. The fact that some of the worms of this table show a 

 greater length than any given in table 1 is because they are speci- 

 mens killed under compression and are consequently unnaturally 

 elongate. I have however admitted them to this table, as the 



