196 HENKY LESLIE OSBORN 



the mouth opening. The spines have a strong affinity for stains 

 and in the iron-haeniatoxyhn preparations are deeply tinged by 

 it, while the cuticle remains unaffected. We know nothing of the 

 process by which spines are formed. 



The principal peculiarity of the wall of Clinostomum is the 

 existence in its inner layer of an extensive system of cavities, an 

 extension of deeper cavities pervading the parenchyma every- 

 where, connected ultimately with the excretory collecting vessel. 

 A full description of these cavities will be given in connection 

 with the excretory system of which it forms a part. They are 

 conspicuous in longitudinal sections and can be seen in fig. 4 G 

 and figs. 6 and 7. The subcuticular cavities run in such a direc- 

 tion as to encircle the body, with connections inward to the col- 

 lecting vessel as seen in transverse sections. 



Organs in the cuticle, perhaps sensory. Certain cavities in the 

 cuticle (see fig. 8) are possibly parts of sensory organs. They 

 can be found in the areas in the oral field immediately around the 

 mouth and on the dorsal surface near the anterior end, but not 

 in the surface generally. In fig. 8 two of these are shown. They 

 are spherical cavities excavated in the substance of the cuticle by 

 which they are entirely enclosed except at the base of where they 

 are open to the parenchyma on which the cuticle rests. The 

 cavities thus have no communication whatever with the exterior. 

 A fine deeply stained fiber can be traced into these cavities from 

 the parenchyma. The indication from views like that of the 

 cavity on the right in the figure is that this thread expands into 

 a disk resting against the upper surface of the cavity. The best 

 interpretation of the function of these organs which we can make 

 on the basis of their structure is that they are the terminations 

 of a pressure sense apparatus, the fiber being regarded as a pro- 

 longation from a more deeply seated nerve cell. 



We have very few references to such organs in the cuticle of 

 other trematodes. They are doubtless not uncommon but not 

 many forms have been examined for them. Nickerson ('95) 

 found a very similar organ in Stichocotyle, one of the Aspido- 

 bothridae. The organ shown in his fig. 15 differs only in size 

 from the one in fig. 8 of this article. Bettendorf also ('97, fig. 



