CESTODA 89 



In addition to the above-named structures, the entire series 

 of joints from the head downwards are traversed by a set of 

 vascular canals, which are doubled in the region of the head. 

 These form the so-called aquiferous system. There are two 

 main channels, one passing down on either side of the worm, 

 both being connected by transverse vessels, which occur singly 

 at one end of every joint. 



The eggs in their mature condition are globular, and contain 

 a six-hooked embryo. They present an average diameter of 

 gg ? of an inch, the shell itself measuring about 5 " in thickness. 

 In 1856 I observed that many of the eggs, whilst still within 

 the uterine branches, displayed an outer envelope, very delicato 

 in structure and totally dissimilar from the egg-shell proper. 

 This has since been more accurately described by Wjeinland, 

 Yan Beneden, and Leuckart. The outer membrane, according 

 to the last-named authority, constitutes the primitive yolk- 

 membrane, within which a part of the yolk-contents separates 

 to form the true egg and embryo by a process of daughter-cell 

 formation. The remaining part of the yolk forms a granular 

 mass, being probably concerned in the ; formation of the true 

 chitinous shell. The true shell displays a series of radiating 

 and circular lines ; the former, however, are more conspicuous 

 than the latter, being due, according to Leuckart, to the 

 presence of a series of fine rod-like chitinous elements, which 

 are formed on the external surface of the original true shell- 

 membrane. The enclosed embryo is furnished with six boring 

 spines, arranged in three pairs, its granular body being invested 

 by an extremely delicate skin-membrane, which is separated 

 from the inner surface of the shell by a clear transparent fluid. 

 The embryo measures ~-^' in diameter. 



The scolex or higher larval stage of growth forms the well- 

 known pork measle or Cysticercus (telce) celluloste of authors. 

 The smallest measles found by Leuckart measured i" in length. 

 They were obtained from the brain, liver, and intermuscular 

 substance of a pig fed with proglottides about thirty days 

 previously. Only those specimens, however, occurring in the 

 liver at this early period displayed an outer membrane proper 

 to the worm itself, the others being simply invested with 

 capsules formed out of the connective tissues of the host. 

 Many measle-masses in the same host were much larger, 

 presenting an average diameter of 5''. The smallest already 

 displayed a smooth, transparent, homogeneous, outer, cuticular 



