414 J- Stäffobd, 



of tlie living' worms for whenever I came upon tliese I liad not the 

 meaiis of measuring them to liand. Of 18 moiinted specimens, re- 

 markably alike in size and shape, the longest measures 9'45 mm 

 by 1'20 mm, wliile the one I have fig-ured was 8-06 X l'o5 mm. 

 I think the living worm mig-ht sometimes measiire iip to 15 mm, 

 the g-reatest length reported for the European species; but as far 

 as I can judge the breadth of this exceeds that of G. cygnoides. 

 The greatest breadth is about tlie middle of the length of the 

 animal from which point it tapers off towards both ends. A most 

 noticeable feature is that the body is quite flat and transparent, so 

 that animals killed in glacial acetic acid and then kept in alcohol 

 permit the chief organs to be distinctly seen without any further 

 treatment. In a series of sections, one selected from the region of 

 the anterior testis measures 1*4 mm broad and '46 mm deep. 

 The thickness decreases slightly from this region backwards 

 and increases forwards tili through the back part of the 

 ventral sucker the worm measures "75 mm in depth but in front 

 of that is becomes thinner again — the body passing gradually 

 into the neck. 



In the specimen figured, which is quite representative, the mouth- 

 sucker measures "465 mm long by "418 mm broad, while the ventral 

 sucker, whose centre is 1"5 mm from the anterior end, measures 

 •728 mm each way. In a sagittal section the ventral sucker is a 

 deep, rounded cup extending more than half way throngh the section. 

 It must be noted that the oral sucker opens downwards and for- 

 wards, so that the measure of the whole length in a mounted 

 preparation is not the true length of tlie sucker, which, counted 

 from the ventral margin of the opening to the posterior end of the 

 sucker, is much less, approximately two-thirds as much. The ventral 

 sucker is normally round, having the same length and breadth, so 

 that the most useful comparison is in the breadths of the two organs. 

 In a good number of cases the ventral measured from l'ö to 1*75 

 times the breadth of the oral sucker. 



In this species the genital organs are very distinct and easily 

 Seen, even in alcoholic specimens that have not been stained and 

 cleared. The great breadth and thinness of its body permit the 

 Organs to lie clear of each other and to be transparent. The 

 lateral shanks of the intestine divide the body, let us say, into 

 thirds — a middle third, which, however, is rather more than a 

 third, lying between the c?eca, and two lateral thirds, left and right, 



