ZooL.— Vol. III.] HEATH— EPIDELLA SQUAMULA. 113 



allow of description, complete the musculature of the pos- 

 terior sucking disc. The cuticular elevations on the under 

 side of the sucker appear to sink into the corrugations of 

 the scales of the host, and thus prevent the sHding of the 

 parasite on the otherwise slippery surface. 



III. The Digestive System. 



As in other ectoparasites, the ahmentary canal consists 

 of three elements, the pharynx, oesophagus, and intestine. 

 In E. squamula the first of these commences with the cres- 

 centic mouth-opening situated on the ventral surface close 

 to the anterior end of the animal. In life the lips are pos- 

 sessed of considerable mobility, but in preserved specimens 

 definite Hp muscles are found to be few in number, and 

 anything of the nature of chitinous jaws or cuticular modi- 

 fications of other kinds is absent. The mouth-cavity 

 likewise is but little developed, and passes insensibly into 

 the space within the pharyngeal sheath whose boundaries 

 are represented in fig. 17. 



As the figures indicate, the pharynx is more or less 

 globular in form, and is composed of several sets of cells 

 of widely different character. Those composing its free 

 extremity (fig. 17, /) number from eight to eleven, and pre- 

 sent a spongy appearance except in the immediate vicinity 

 of the nucleus where the protoplasm becomes more com- 

 pact. Imbedded in these larger cells are a few relatively 

 small nuclei belonging apparently to interstitial cells, but 

 owing to the lack of definite characters and to the indis- 

 tinctness of the boundaries between the cells of this region, 

 it becomes impossible to determine their exact nature. Im- 

 mediately below the cuticle which covers the free extremities 

 of these cells is a layer of circular muscles whose contrac- 

 tion in cooperation with similar muscles in other parts of 

 the pharynx results in protracting the latter a short distance 

 through the mouth-opening. 



The cells of the second type (fig. 17,/") are situated im- 

 mediately behind those just described, and are at once 



