in ANATOMY OF CESTODA 85 



be found, the larva of Schistocephalus solidus Crepl., which occurs 

 in the intestine of Terns, Storks, Mergansers, and other birds. 

 Species of Ligula are found in the same birds. The intestine 

 of a Lophius or Cyclopterus (" lump -fish ") contains, usually, 

 the early and intermediate stages of various Cestodes, while 

 the alimentary canal of Elasmobranchs often contain many 

 peculiar Tetrarhynchidae and other forms. For the study 

 of development, the Taenia anatina from the duck may be 

 used. The ripe proglottides are collected, and the eggs placed 

 with Cypris ovum in an aquarium, with the probability that 

 some of the embryos will enter the Ostracod, and the peculiar 

 Cysticercoid may be bred. 1 Cysticercus pisiformis and Coenurus 

 serialis, which occur commonly in rabbits, are also suitable 

 objects for examination. 



A Cestode such as Calliolothrium (Fig. 36) is divisible 

 into head and proglottides. Moniez has suggested that the 

 head is really the morphologically hinder end of the body, in 

 which case the formation of proglottides would closely resemble 

 the mode of segmentation of an Annelid larva. The close 

 similarity, however, between the Cysticercoid larva (Fig. 43, F) 

 and the Cercaria of a liver-fluke, seems to show that the anterior 

 end is the same in both cases, and since it bears the central part 

 of the nervous system, we may reasonably call it the " head." 

 Moreover the hinder end of a Platyhelminth usually possesses 

 the chief excretory pore. Another difficulty is the determina- 

 tion of dorsal and ventral surfaces. Authors are agreed, on 

 the analogy of Trematodes, in which the testes are usually dorsal 

 and the ovaries ventral, that the dorsal and ventral aspects of a 

 Cestode are determined by the position of these organs, although 

 the often radially formed " head," the lateral or superficial posi- 

 tion of the genital apertures, and the variability of these features, 

 render it a matter of considerable doubt whether " dorsal " and 

 "ventral" are more than useful conventional terms. The 

 suckers and hooks are borne on a muscular cap, the " rostellum," 

 which is only slightly developed in the Ichthyotaeniae. The 

 body is solid, and is divisible into an outer muscular coit 

 enveloped in a (possibly epidermal) investing membrane and 

 an inner parenchymatous tissue containing the chief part of the 

 excretory, nervous, and reproductive systems. One or two pairs 

 1 Schmidt, Arehiv f. Naturgcschichte, Jahrg. Ix. Bd. 1, 1894, \>. 65. 



