102 THE CESTOIDEA 



or " head " of the Merozoa are posterior. There seems to be no 

 a priori reason why an organ of fixation, varied in character as it 

 is in the Monozoa, should not occupy different positions in the 

 different genera. But although we may conclude that in Amphilina 

 the sucker is morphologically posterior, that in Gyrocotyle it. is anterior, 

 and that the mobile organ of Caryophyllaeus is also anterior, it has 

 been considered desirable, while drawing attention to this com- 

 parison between the " Archicestode " and the Trematode, to preserve 

 the usual terminology and mode of representation. 



The excretory system of Caryophyllaeus consists of a super- 

 ficial network of capillary vessels (Fig. II. 5, 6, 7), bearing 

 numerous flame-cells, and communicating with certain larger canals 

 lying in a deeper plane the " ascending canals " of which there 

 are a dorsal and a ventral on each side ; they pass forwards into 

 the neck, where they unite to form a single lateral vessel on each 

 side, which enters an elaborate plexus in the mobile organ ; from 

 this plexus ten " descending canals " pass backwards, connected 

 here and there by transverse vessels, to open into a median con- 

 tractile sac at the posterior end of the body, which communicates by 

 a terminal pore, as in the Malacocotylea. This is essentially the 

 plan of this system throughout the class. In " Archigetes " it is 

 stated that there are only eight descending canals. We know 

 nothing of the system in Amphilina. In Gyrocotyle the system is repre- 

 sented by a network only, without main canals, opening by two pores 

 (as in Heterocotylea) ; and whereas in the Cestoidea in general flame- 

 cells have been recognised in the outer layer of the parenchyma, 

 Spencer was unable to detect any in Gyrocotyle ; but many of the 

 larger canals of the excretory system are provided with a continuous 

 row of cilia on one side. 



The nervous system in Caryophyllaeus consists of a pair of deep 

 lateral nerves, with four dorsal and four ventral more superficial 

 nerves. All are connected anteriorly by a ring-shaped " cerebral 

 commissure," but without special accumulation of ganglion cells 

 here. Anteriorly, nerves go to the mobile organ ; and posteriorly 

 the lateral nerves unite around the excretory pore. 



In Gyrocotyle and Amphilina (Lang, 20) a more or less laterally 

 placed pair of nerves runs along the body, united at each end of 

 their course. 



Very little is known about the life -history of the Monozoa. 

 Caryophyllaeus passes the earlier part of its life in the coelom of 

 Tubifex (D'Udekem, 1855). Here, while retaining a "caudal 

 vesicle " with six booklets, it grows to a considerable size, and its 

 genital organs become fully developed, though we have no evi- 

 dence that eggs are fully formed while in this host, as those 

 of " Archigetes " are stated to do ; the worm must be swallowed 

 by a carp, roach, etc., when the Caryophyllaeus becomes mature in 



