11AMIFICATION OF THE EXCKETORY VESSELS. 301 



circular muscles of the body which surround it, and are thus able to 

 cause it to contract. 1 



What I have said above as to the excretory apparatus of the Ces- 

 todes is primarily applicable only to those species with four suckers. 

 In Bothrioceplialus, which has only two suctorial grooves on the surface 

 of the head, the structure of the canals is somewhat different, since the 

 longitudinal canals are not only increased in number, but are very 

 thoroughly connected by numerous transverse and oblique anastomoses, 

 which are" quite independent of the joints and 

 form a more or less close mesh work. Usually 

 there are eight of these longitudinal vessels, 

 which are equally distributed on either side, but 

 there are cases where sixteen and even more ap- 

 pear, though not all necessarily of the same size. 

 Towards the head, these canals usually run to- 

 gether till only two main stems are left. It is 

 doubtful whether these are united in a loop, as 

 in Tcenia, but in some species at least this is 

 not so. At the posterior end one finds a FIG. 155. Excretory ap- 



r paratus of Bothnoccphalus 



distinct opening in the form of a bowl or probostideus, after Steu- 

 bladder-like depression into which the longi- dener - ( x 32 -) 

 tudinal canals run. This structure is most conspicuous and inde- 

 pendent in Caryopliyllceus, which, as is well known, has no joints, 

 and in which, therefore, the posterior extremity is permanent. It has 

 formed a longish tube, which exhibits a distinct pulsation effected by 

 the musculature investing its cuticle. 2 



The above-mentioned network of vessels is not the only structure 

 of the kind to be found in Botliriocephalus. In small transparent 

 worms, which can readily be investigated alive, one can convince 

 oneself of the existence of a system of fine, richly ramified and 



1 Wagener describes special excretory openings in the anterior end of many Cestodes 

 (" Entwickelung d. Cestoden," Breslau, 1854: Nova Acta Cces.-Lcop. Acad., Bd. xxiv., 

 Suppl. ), which are connected with the longitudinal vessels by short cross branches. Both 

 Kolliker and I think we have occasionally observed these openings. Hoffman has lately 

 described similar openings in Tetrarhyncltus, not, however, behind the suckers, but before 

 them, and in fewer numbers also on the anterior lateral borders ("Ueber den encys- 

 tirfcen Scolex von Tetrarhynchus," Niederldnd. Archiv f. Naturw., Bd. v., Heft. L, p. 1, 

 1879). [The investigations of Fraipont (Archiv. d. BioL, t. ii , p. 10, 1881) have shown 

 that such secondary openings are by no means uncommon in tape-worms. In Ligula, 

 where Riehm (Corresp.-BL d. Natunc. Ver. f. Sachsen u. Thiiringen, p. 276, 1882) observed 

 them, they were arranged in regular metameric fashion. Pintner (loc. cit., p. 31), in con- 

 tradiction to the above, remarks that the longitudinal vessels always open singly at the 

 hinder margin of the joints. R. L.] 



2 According to Steudener, this funnel-shaped organ is, even in the case of Caryophyl- 

 I&us, only a depression of the posterior extremity. 



