335] PSEUDOPHYLLIDEA FROM FISHES— COOPER • 47 



ring-like layer of loosely arranged main longitudinal fibres occupying the 

 middle one-third of the radius of the nearly circular cross-section; no trans- 

 verse fibres; but comparatively strong cuticular muscles, of which the inner 

 longitudinal layer is the more pronounced. Farther forward this main longi- 

 tudinal group gradually gives off small fibres towards the cuticula as they them- 

 selves diminish in number and size, until at the level of the hinder ends of the 

 bulbs only a few of the latter fibres are left just beneath the subcuticula. An 

 outer series at the same time forms a compact layer situated close to the longi- 

 tudinal cuticular fibres (and hence outside of the subcuticular nuclei) but 

 separated from them by a thin stratum of circular fibres. And this continues 

 to the tip of the scolex, most of the remaining inner longitudinal muscles being 

 located at the ends of the transverse and dorsoventral diameters of the transec- 

 tion. In the region of the bulbs the body wall is thus quite muscular, and in 

 all probability assists the bulbs in evaginating the proboscides by compressing 

 the whole of the parenchyma g\irrounding them. Between the bulbs and right 

 beneath the tip of the scolex a few transverse and sagittal fibres are to be found, 

 while just beneath the bases of the stumps of the proboscides the outer longi- 

 tudmal muscles unite with the longitudinal cuticular fibres to form H -shaped 

 loops surrounding the diagonal quadrants of the scolex which accommodate 

 the bulbs. These loops are evidently for the control of the direction of the 

 proboscis stumps. 



Owing to the fact that, as originally stated by the writer (1914a:96), "there 

 is a more or less definite point in the strobila, at or about the 15th proglottis, 

 ahead of which the genital organs do not seem to develop and behind which 

 in older strobilas they appear very quickly, " and the further fact that not only 

 do the auricular appendages of the posterior ends of the proglottides disappear 

 at about the same place constantly, namely, at about the 23rd or 24th segment, 

 it might seem that the (secondary) strobila is composed of a more or less 

 definite and predetermined number of segments. But this is not the case, 

 as will be seen presently when the method of formation of new proglottides 

 is described. As a matter of fact segmentation in this species is carried on 

 after an entirely novel plan, involving the formation of not only new segments 

 but whole chains of them or, indeed, whole strobilas from the original larval 

 or primary strobila as it is here called. 



The original larva which resembles the bothriocephalid plerocercoid, 

 excepting for the peculiar scolex, gradually elongates with growth, until 

 between a length of 4 or 5mm. the first traces of segmentation appear in the 

 hinder ends of cleared specimens as feeble aggregations of nuclei forming faint 

 dark lines at regular intervals. In one specimen 4.8mm. in length five intervals 

 were made out, the second last of which was 0.37mm. in length by 0.20mm. 

 in diameter, while the last one was shghtly larger and rounded posteriorly. 

 These primary segments elongate with the growth of the strobila, and the 

 constrictions between them gradually deepen as their anterior and posterior 

 ends enlarge shghtly, the former relatively faster than the latter. When a 

 total length of strobila of about 10mm. is reached, the hindermost segment, 



