710 THE ANATOMY OF BOTHRIOCEPHALUS LATUS. 



situated, the shell exhibits for a while a fissure, which is closed at a 

 later stage by the application of a new portion of shell - substance, 

 which always remains isolated. The young shell is brighter and 

 thinner than it subsequently becomes, so that a staining fluid rapidly 

 affects the contents, which no longer happens in the deep - brown 

 older eggs. 



Clear and distinct as the processes of oogenesis are in suitable 

 preparations, the actual mechanism eludes observation. It seema 

 plausible, however, that it is the pressure of the surrounding canal 

 which forms the eggs, though the absence of a special musculature 

 in the uterus does not seem to agree with this supposition, nor the 

 fact that the eggs in process of formation do not occur singly, one 

 behind the other, but usually in considerable numbers on the same 

 transverse section. It is possible that special protoplasmic activities 

 (amoeboid movements) play some part in the process. 



The mature ova exhibit, in form and size, several more or less 

 striking peculiarities, and that quite apart from the not unfrequent 

 occurrence of malformed or stunted specimens. These variations 

 are especially noticeable in the eggs within the lower uterine 

 coils, so that it seems as if they become more uniform the longer 

 they remain within the uterus. In the rosette they have usually 

 a longer diameter of 0*05 mm., and a shorter of 0*035 mm. ; but 

 diameters of 0'056 and 0'04 respectively are also not unfrequently 

 present, so that in shape they appear sometimes more elongated, some- 

 times rounder. The lid is seldom recognisable without pressure to 

 cause it to spring up. It lies at the anterior pole, which is occa- 

 sionally somewhat flattened, and possesses a diameter of 0'013 mm. 

 (Fig. 359). 



What I have noted above in regard to the reproductive organs 

 relates primarily only to the state of the ripe joints, which form, as 

 we know, the great majority in Bothriocephalus latus. In a fresh 

 specimen, measuring 720 cm. in length, the number of joints was 

 about 2400. The unripe joints are, indeed, present in considerable 

 numbers (at least 500 to 600). They are characterised by the absence 

 of hard-shelled ova, and afford in their adolescent stages a complete 

 survey of the various stages in the formation of the generative organs. 



The Development of the Reproductive Organs commences with an 

 extremely simple structure. It consists, as in the Tseniadae, of an 

 aggregation of small nucleated cells, occupying the centre of the 

 joint, and but slightly separated from the surrounding parenchymal 

 cells. It is recognisable at a very short distance behind the head, so 

 that it seems probable that the differentiation of these cells has already 

 occurred in the very earliest joints. At first of inconspicuous size, 



