BY WILLIAM A. HASWELL. 663 



The scolices of Schistocejjhalus and Ligula, then, would seem to 

 be the nearest known allies of the parasite under examination. 

 Tliese are elongate, ribbon-like, segmented, and notched at the 

 anterior end. They are found in certain special situations in the 

 body-cavity of Cyprinoid fishes, and, unlike most scolices, when 

 ready for their final transformation into the mature tape-worm, 

 perforate the wall of the body of their host by their own efforts, 

 and pass out into the water, whence they are taken up into the 

 alimentary canal of some water-bird, in which they complete 

 their development. Before proceeding with the comparison of 

 the pai-asite of the Hyla with Ligula and Schistocejjhalus I shall 

 give a detailed account of my observations on the minute structure 

 of the former, as some of these are of importance as bearing on the 

 question of affinities. 



The whole surface is covered with a chitinous cuticle (fig. 3, cut), 

 which consists of two layers, an outer thinner and an inner thicker. 

 The outer layer is a homogeneous membrane in the anterior part of 

 the body of my best-preserved specimen, while further back it is 

 divided by numerous vertical fissures, so that in section it has the 

 appearance of being composed of numerous close-set papillae. The 

 inner thicker layer is perfectly homogeneous. Beneath it is a thin 

 layer of minute highly i-ef racting bodies (x), which are apparently 

 nothing else than thickened and specialised outer ends of the 

 fil)res of the parenchyma muscle, which are found to be continuous 

 with them ; and these bodies seem to be attached to an exceedingly 

 thin continuous layer of similar appearance which immediately 

 underlies the cuticle. The fibres of the parenchyma muscle would 

 thus appear to be inserted not directly into the cuticle, but into a 

 thin membrane — perhaps of elastic character — immediately under- 

 lying the latter. 



At a little distance below this is an irregular layer (ep), of 

 tolerably large nuclei, each having around it a small quantity of 

 protoplasm which sends out slender fibre-like processes inwards 

 and outwards. This layer doubtless represents an epithelium of 

 vertically elongated cells of which the bodies are imperfectly 

 developed or have become attenuated. 



