264 Mr. W. Nicoll 07i the 



The testes are small longitudinally oval bodies, situated 

 to the outer side of the excretory tubes and on a level with 

 the posterior border of the ventral sucker or slightly further 

 forward. They are symmetrical about the middle line and 

 measure 'llX'OS mm. The ovary is a short distance in 

 front of the right testis, on the level of the anterior border 

 of the ventral sucker. It is round and slightly larger than 

 the testes. The position of the yolk-glands is almost in- 

 variably in front of and dorsal to the ventral sucker. 

 Occasionally they are a little further back, but in only one 

 instance were they found beyond the centre of the sucker. 

 They are symmetrical about the middle line and consist of a 

 number of small loosely-knit follicles. 



The uterus is confined to the space between the two 

 suckers. In one case out of sixty a few ova were observed 

 behind the ventral sucker on the left side, and this was the 

 case in which the yolk-glands were so far back, thus it must 

 be regarded as abnormal. The ova are light yellow and 

 fairly numerous. They present one of the most peculiar 

 features of the animal, and it is surprising that no mention 

 has been made of a similar peculiarity in connection with 

 the other species of the genus. It consists in the presence 

 in the same specimen of ova of very different sizes, tlie 

 largest being as much as eight times the size (volume) of 

 the smallest. This, moreover, is not a rare occurrence, but 

 is to be met with in almost every other specimen. In several 

 instances hardly any two ova were of the same size, and 

 almost every length between a minimum of '012 mm. and a 

 maximum of "031 mm. was observed. The smallest ova dis- 

 played a fairly constant size of '012 x '009 mm., while what 

 may be assumed to be the normal ovum {i. e. such as was 

 found in an example possessing ova of nearly uniform size) 

 measured •025-"031 x 'OIZ-'OIO mm. This corresponds fairly 

 well with the size of the ova in G. bursicola. No explanation 

 of this apparent vagary suggests itself at present ; the pheno- 

 menon is unique, to my knowledge. It can hardly be the 

 case that the ova when first formed are of small size and 

 grow in the course of their passage through the uterus, for 

 the small ova are found throughout the latter even near its 

 termination ; in addition the shell is of a bright yellow 

 colour, which is not usually the case in newly-formed ova. 

 Many large colourless ova are also sometimes to be seen in 

 the vicinity of the ovary. The condition is much more 

 probably pathological, but its occurrence in so many speci- 

 mens seems opposed to this view. 



The vesicula seminalis is a large ovoid body on the left of 



