STRUCTURE OF CLINOSTOMUM 199 



eter. The oblique muscles running in the usual two directions 

 are more deeply located. 



Certain interesting points were noted in the cytology of the 

 body wall muscles which will receive attention later in connection 

 with those of the parenchyma. 



Wall structure iri the oral field. The wall of the oral field pre- 

 sents a structure decidedly unlike that of the general surface of 

 the body. Figs. 3 and 5 show the wall under low magnification. 

 It is very much thinner, owing to the great reduction of all its 

 components. The cuticle becomes so thin as to be barely recog- 

 nizable. The spines, which are so general over the rest of the 

 surface of the animal, are entirely wanting on the oral field with 

 the exception of a small area immediately around the nlouth 

 opening where spines of a much smaller size exist. Sub-cuticular 

 cavities so conspicuous elsewhere are scarcely recognizable. They 

 do not in any case take on the regular arrangement so usual else- 

 where in the body wall, but are merely irregular cavities under- 

 lying the surface and communicating internally with the vessels 

 of the excretory system. The musculature of the oral field does 

 not agree with that of the rest of the body. The various layers 

 are not continued from the wall into the field. Fibers can be 

 found lying parallel with the surface but they cannot be con- 

 nected with the fibers in the wall beyond. The longitudinal mus- 

 cles of the parenchyma (p7nl in fig. 3) run on anteriorly until 

 they meet the surface of the field to which they are then vertical. 

 They are shown in fig. 5 at ml running directly to the wall, their 

 position enabling them to act as retractors of the field as shown 

 in the figure. 



Glands (?) in the body wall. There are certain nucleated cells 

 lying in the body wall, as shown in fig. 7 at gl, which seem to be 

 probably of a glandular nature. They are very long and slender, 

 consisting of a globular body, which lies on the level of the oblique 

 wall muscles, and a tapering portion which can be traced outward 

 to a termination on the inner surface of the cuticle. The outer 

 end of the cell may branch so as to present in sections two termi- 

 nations. No passage through the cuticle has been seen or any 

 indications of secretions passing from these cells to or through it. 



