NATURE OF THE CUTICLE. 285 



composition, but is perfectly homogeneous. Both in this respect and 

 in its chemical composition (as shown with regard to Ecliinococcus) 

 this skin reveals its essentially cuticular nature. The thickness 

 of this cuticle varies exceedingly, and not always in proportion to 

 the size of the animal, although as a rule the larger species have 

 the thicker covering. It ought not, of course, to be overlooked that 

 the thickness and firmness of the cuticle is very different at different 

 parts of the body. The cuticle is thickest in the bladder-worm of 

 Tcenia echinococcus, which sometimes grows to the size of a child's 

 head, or even larger. In this case it shows a very striking lamination, 

 often hardly perceptible in other cases. When the cuticle attains a 

 certain thickness, it possesses a more or less distinct vertical striation, 

 which is, of course, fine, and only visible by the use of a high power. 

 This is of great importance, however, for these organisms, since it is 

 caused by the presence of thickset pores, by means of which the 

 absorptive power of the skin the only absorbing organ in these 

 asplanchnic Cestodes is greatly increased. The pores can some- 

 times be observed on surface inspection as fine, thickly studded little 

 points, some bright, some dark, according to position of the microscope- 

 tube. 



We owe the detection of these pores to the researches of Sommer 

 and Landois, whose results have been fully confirmed by subse- 

 quent observers. All unite, too, in emphasising their nutritive im- 

 portance, but this is represented in a way which I cannot but con- 

 sider erroneous. According to this theory, the pores are not in them- 

 selves directly efficient in nutrition, but only in so far as they serve 

 for the protrusion of fine protoplasmic threads, which are in direct 

 continuity with the subcuticular tissue to which they thus pass on 

 the food. This theory is especially maintained by Schiefferdecker, 

 who has tried to establish it to the minutest details. 



In suitable preparations it is not difficult to observe, as I have 

 myself done in my earlier investigations, that the cuticle, when intact 

 arid of considerable thickness, bears, at certain intervals, a fringe of 

 fine rods or threads. These are about as long as the cuticle is thick, 

 have a granular nature, and " forcibly remind one of similar structures 

 sometimes exhibited on the outer surface of intestinal epithelial cells 

 in Mammalia." 1 They are not unfrequently "so thick that they 

 look as though the outer surface of the worm were covered with 

 a thin layer of granular protoplasm." 1 I attached no special physio- 

 logical importance to these structures, simply because I could only 

 regard them as anatomically very unimportant, namely, as the re- 

 mains of an older exfoliated and altered cuticle, or, in other words, 



1 Quoted from Landois and Sommer (loc. tit.). 



