PROTEOCEPHALUS AMBLOPLITIS LEIDY 185 



SESSIONAL PAPER No. 39b 



be concluded that these spaces are filled with chalk bodies; it is quite probable 

 that they accommodate oil-globules (LaRue). Furthermore, in plerocercoids from 

 the ovaries or testes of the black bass where they are richly supplied with food, 

 these spaces are very numerous, quite large and crowded closely together. It is 

 doubtless their distension with fat which causes the well-nourished appearance of 

 these larvae as mentioned above. 



Subcuticula or Absorptive Cells. — The subcuticular cells are quite granular 

 in consistency and possess comparatively large nuclei which stain deeply with 

 Heidenhain's iron-haematoxylin stain (PI, XXI, Figs. 12 and 13). Centrally they 

 are more or less abruptly attenuated, thus not proceeding far into the cortical 

 parenchyma with processes of whose cells they mingle and anastomose. Including 

 these attenuations as far as they may be distinctly traced with a magnification of 

 450 diameters, the cells average 20fi in length. Their peripheral ends are truncated, 

 slightly expanded and apparently closely applied to the outer circular layer of 

 muscles, while the longitudinal cuticular muscle fibres penetrate their broad bases 

 some little distance from the latter. However, in gaps in the layer of circular 

 muscles the absorptive cells are seen to proceed farther out as fine processes which 

 can be distinctly traced as such into the cuticula for at least one-third of its thick- 

 ness. Furthermore, it is quite likely that these processes proceed farther out, 

 perhaps as far as the boundary between the two layers of the cuticula, as described 

 below, but the highest powers used did not show this positively. A study of better 

 sections with various kinds of fixations would doubtless much elucidate this prob- 

 lem which has occupied the attention of so many workers during the past. 



Cuticular Muscles. — The cuticular muscles are quite typical in their structure 

 and arrangement and closely resemble those figured by Benedict for the adult 

 P. ambloplitis They are shown in various figures, especially in PI. XXI, Fig. 13. 



Cuticula. — By the use of the iron-haematoxylin stain the cuticula is resolved 

 into two distinct layers, the outer of which takes no stain as compared with the 

 inner. The latter (PI. XXI, Fig. 13 cu") is about four times as quick as the former, 

 and takes the stain better in its outer parts. But in deeply stained series the 

 inner portions show the structure described above under the subcuticula. In the 

 middle third of the cuticula, which takes the stain well, what appear to be fine 

 processes from the absorptive cells become arranged in a more or less parallel man- 

 ner and extend to the boundary between the two layers where a layer of compar- 

 atively large granules, quite regularly arranged, is plainly to be seen. Beyond 

 this the cuticula appears to be quite homogenous with the highest powers of magni- 

 fication available. The parallel processes, however, are identified more by small 

 spindle-shaped granules placed along their courses than by the parts of what must 

 be canals between these enlargements. Thus it seems that the outer homogeneous 

 layer of the cuticula is something quite different from the inner layer although it 

 takes a transparent counter-stain like Orange G. to the same extent as the latter. 

 Concerning the significance of these layers, the extent of the present work will not 

 permit the making of any definite statements. It seems, however, that the external 

 layer of the cuticula is a definite structure and not something added from the out- 

 side since it is of uniform thickness, excepting where broken by injury, and has a 



