ii8 THE CESTOIDEA 



sented by a slight pit in Ligula, and in Triaenophorus by a wide, 

 shallow depression. An accessory sucker, such as frequently occurs 

 in the Tetraphyllidea, is met with in Amphicotyle, above the limits of 

 the bothria. An extension of the bothria round the scolex, and their 

 fusion, may lead to the condition in Cyathocephalus, wnere a circular 

 disc is formed, capping or surrounding the scolex. Modification in 

 another direction, viz. by the union and coalescence of the lateral 

 lips of the bothrium, leads to the formation of a dorsal and a 

 ventral tube, as in the Solenophoridae ; by the closure of the 

 lower aperture in Diplocotyle, two " suckers " are simulated ; and in 

 Duthiersia the upper opening is expanded, and the whole sides much 

 folded to form a very mobile organ recalling the "phyllidium" of 

 the Tetraphyllidea. Further, in a few cases, booklets are carried 

 oy ihe scolex ; these aid very materially in fixing the parasite to 

 the wall of its host intestine. The scolex may be prolonged beyond 

 the bothria, to form a " rostellum," which in Ptychobothrium is long 

 and mobile ; and in Schistocepl talus is provided with a small pit, 

 recalling the terminal sucker of other orders. Indeed, as will be 

 seen below, modifications and differences of the same character as 

 these occur again and again in different orders of the Merozoa. 

 The typical " proglottidisation " is not expressed externally in 

 Ligula and Triaenophorus, though the genital pores indicate the 

 repetition of the genital organs (Fig. XV.) ; in other cases, also, the 

 demarcation of the proglottids is but feebly expressed (Cyatho- 

 cephalus and Diplocotyle). 



The copulatory pore, though typically ventral, may move out- 

 wards so as to become marginal (Fig. III. 5), and may even come to 

 lie on the dorsal surface in Ptychobothrium. But these differences in 

 position seem scarcely sufficient, by themselves, to justify new genera, 

 and far less new families; and it is a matter of speculation as to which 

 is the more primitive position. Throughout this order the penis 

 opens into the genital atrium in front of the vagina ; and as a rule 

 the birth-pore is behind the copulatory pore, but the reverse holds 

 in Bothriotaenia. 



BRANCH B. TETRABOTHRIDIATA. 



Cestoidea Merozoa, in which the scolex is provided with four organs 

 of adhesion (? or locomotion), and in which the uterus is a closed sac, so 

 that the eggs can escape only after the decomposition or rupture of the 

 proglottid. 



The branch includes four orders (families of van Beneden) founded 

 chiefly on the character of the organs of the scolex : Tetraphyllidea, 

 Diphyllidea, Tetrarhyncha, Tetracotylea, 



ORB*;* 1. Tetraphyllidea, v. Ben. ( = Tetrabothridae, Diea). 



Tetrabothridiate Cestoidea in which the organs of the scolex are 

 outgrowths from it; these "phyllidia" are more or less, but always 



