On Sticliocotyle nepliropl.t Cunniiighnni, a piirasite of the American lobster. 457 



already pointeii out, an average thickness of from 8 to 11 ^u, which 

 is a rather remarkable developuient when the small size of the worm 

 is taken into consideration. 



The conclusion, therefore, to which 1 have come concerning the 

 outer covering of the i)ody is, that it is neither a basement membrane, 

 nor an epidermis from which the evidences of cellular structure have 

 been lost, nor yet a secretion produceil by certain specially modified 

 gland cells. I hold it to be formed material, which is produced in 

 all peripheral i)ortions of the body in connection with the trans- 

 formation of the unmodified peripheral cells into the highly vacuolated 

 parenchymatous tissue. This formed material makes its way in minute 

 globules, through the two muscular layers of the body wall and the 

 cuticula already deposited, to the exterior, where in contact with the 

 surrounding water it assumes a somewhat gelatinous consistency and 

 becomes added to the outer surface of the cuticula already present. 



Musculature. 



Immediately beneath the cuticula lies the musculature of the 

 body- wall. This is made up of three sets of fibres, all lying parallel 

 with the surface: circular, longitudinal and oblique (PI. 30, Fig. 9). 

 The most numerous of these are the outer circular fibres, which form 

 a close layer; when the worm is in a contracted condition the fibres 

 are so closel) appressed that they become flattened by mutual pres- 

 sure. In a moderately elongated worm, however, the individual fibres 

 appear separated from one another by narrow spaces and then they 

 are circular in cross section. 



The next deeper layer is composed of fibres extending lengthwise 

 of the body and hence crossing those of the outer layer at right 

 angles. They are much less numerous than the circular muscles and 

 the individual fibres are larger. 



The deepest layer, composed of diagonal fibres, is scarcely recog- 

 nizable as a distinct set of muscles; it is made up of numerous 

 fibres of varying degrees of obliquity forming an almost perfect trans- 

 ition from the longitudinal to a very oblique course. The fibres of 

 this system are about equally divided betw^een those that extend 

 forward obliquely from right to left, and those from left to right; 

 and in the normal degree of contraction of the worm these cross one 

 another at right angles. Their degree of obliquity , as well as the 

 angle at which they cross one another , is, however, dependent upon 

 the state of contraction of the body. 



Zool. Jahrb VIII AWth. f Murph. 3Q 



