and drawings of it among P. integer rimum are too schematic. The at- 

 taching armature of the disc of the larva is represented by 16 edge hooks 

 and a pair of middle hooks (Fig. 205). The edge hooks are of the typical 

 shape with a well-expressed transversal growth between the terminal 

 hooks and the handle. The middle hooks have the shape of small chitinous 

 little parentheses of smaller sizes than the lateral hooks. The length of 



the edge hooks is 0. 028 - 0. 032 mm and 

 of the middle hooks 0. 018 - 0. 02 mm. 



After its attachment to 

 the gills of the host and loss of the 

 ciliary epithelium the fate of the 

 larva is twofold. In the case of 

 accelerated growth, the formation 

 of the gill form (see page 121 and 

 Fig. 127), its metamorphosis is 

 Fig. 205. Polystoma integerrimum acconnpanied by intensified feeding, 

 Froelich, attaching disc of a free- in connection with which the intestine 



swimming larva. Strongly com- grows considerably. The latter 



pressed. acquires sac-like form with vague 



outgrowths along the exterior edge and a 

 few interior anastomoses. The posterior end of the intestine extends into 

 the attaching disc cind even occupies a large part of it. The sex system of 

 the type different than the one which parasitizes the urinary bladder 

 develops quickly. Its basic peculiarities are: a strongly elongated and p. 185 



sausage -shaped ovary; the absence of vaginal ducts and of the ductus 

 g enito - inte s tinali s ; the absence of the uterus proper and the presence only 

 oi the ootype in which the eggs are formed one at a time; and finally the 

 presence of one testis of a rounded form. The attaching disc grows un- 

 equally. The lateral hooks remain without change in shape and size, 

 whereas the middle hooks grow relatively little reaching 0. 04 - 0. 045 mm 

 in length, and do not form any offshoots. Subsequently starting from the 

 posterior end of the disc, suckers are incepted at the places of 3 pairs of 

 lateral hooks (6th, 5th, and 4th) in such a fashion that the lateral hooks 

 eventually are located in the centers of the sucker. For the most part, 

 the sizes of the suckers remain unequal during the entire life of the worm, 

 the posterior are larger and the anterior are smaller. The attaching disc 

 is often strongly deformed and has an irregular shape, depending to a 

 great degree on the size and nature of the gill cavity of the host. Among 

 the larvae which develop into the adult form in the urinary bladder the 

 development takes place much slower and the worms reach their final 

 structure only in the second year of their life in contrast to the gill forms 

 all the development of which takes place within a few weeks. The larva 

 begins its metamorphosis on the gills of the tadpoles succeeding largely in 

 forming the first and second pair of suckers. It is true that these suckers 

 do not as yet have the final form and dimensions (Fig. 206, A and B). At 

 the sanne time with the metamorphosis of the tadpoles and the loss of the 



200 



