22 ILLINOIS BIOLOGICAL MONOGRAPHS [22 



considered as functional. Since ripe proglottids are shed after or about 

 the time that the eggs are ripe one frequently encounters strobilas which 

 lack the end proglottid. The loss of this proglottid is not to be consid- 

 ered as a special character, for it is common to many eestodes outside 

 the group. 



Two pairs, dorsal and ventral, of main lateral excretory trunks ex- 

 tend through the strobila. Of these the ventral vessels are the larger. 

 Some additional longitudinal vessels have been described by von Linstow 

 (1891) in Proteocephalus longicollis. It seems probable that he saw the 

 cut ends of branches and anastomoses. Some species have a commissural 

 vessel connecting the ventral excretory vessels at the posterior end of the 

 proglottid. It has not been noted in other species. In the neck region 

 and throughout the strobila many small branches arise from the ventral 

 vessels and some also from the dorsal vessels which pass to the surface 

 of the worm where they discharge to the exterior through a small pore. 

 These openings occur more fiV^uently on the ventral surface but may 

 be found on the lateral edga^ In most species they are irregularly dis- 

 tributed but in Corallohothnum lohosum Riggenbach (1896) found that 

 they regularly came to the exterior at the posterior comer of the pro- 

 glottid. This finding has not been supported by subsequent work on 

 other species. In the head and the anterior neck region there are 

 numerous coils of vessels and anastomosing branches of the same which 

 extend well into the tip of the head. These coils lead back and are con- 

 nected with the main lateral excretory trunks. At the posterior end of 

 the worm the excretory vessels discharge, if the end-proglottid is pres- 

 ent, through a common excretory pore (Fig. 51). Just anterior to this 

 pore and discharging thi;ough it is sometimes a pulsatile bladder which 

 is most readily seen in the plerocercus. The flame cells at the ends of 

 minute vessels which discharge into the main vessels or into the larger 

 branches are situated in the medullary parenchyma not far from the 

 main excretory vessels. They have not been found in the cortical paren- 

 chyma nor in the mid-field of the proglottid. Their distribution in 

 Ophiotaenia filaroides and Proteocephalus amhloplitis has been thoroly 

 worked out (La Rue 1909). 



The cuticula and the subcuticular structures are scarcely worthy of 

 discussion here for in details of structure they do not differ from other 

 eestodes. In the Acanthotaenia alone are there special features of the 

 cuticula to which attention should be called. Here the cuticula is thrown 

 up into minute cuticular spines which are too minute to be called hooks 

 or booklets. This condition is most prominent on the head and neck 

 but may also occur to a smaller extent over the cuticula of the entire body. 

 These features have been emphasized by von Linstow (1903) and John- 



