COVERING-CELLS AXD CILIA. 



327 



external egg membrane has by this time increased to about 0*06 mm., 

 a considerable space is left between it and the fringe, and this is 

 occupied by the covering-cells, which have also increased in size and 

 proportion to the egg, and are generally so closely packed together, 

 that they are flattened at their points of contact. The original 

 albumen has gradually contracted into the so-called " granular mass." 

 This generally assumes a spherical form, and inserts itself here and 

 there between the covering-cells, and during the growth of the embryo 

 gradually deposits within itself a number of coarse shining granules 

 and fat-like drops. 



After a long stay in the ovary, the covering cells not unfrequently 

 lose their external boundary and are destroyed. Their contents have 

 generally previously assumed a finely granular nature, and in this 

 form can usually be demonstrated for a time lying round the embryo 

 with its vesicular nuclei. This is especially the case in Tcenia serrata, 

 whose covering cells are very considerably smaller than those of T. 

 maryinata and T. saginata. 



The first indications of the embryonic hooks in Tcenia solium and the 

 related forms appear after the formation of the egg-shell, and at about 

 the same time at which the first protuberances are observed upon the 

 shell. They are at first little points, situated on the outer surface of 

 the embryo, which is covered by a soft skin ; and, like the hooks of 

 the tape-worm, they become independent organs, only by the growth 

 and development of the radical process. 



Histologically, the adult embryo exhibits only a slight advance 

 upon its former state. It apparently consists of a uniform, clear sub- 

 stance, in which one can distinguish at 

 most only a number of granular deposits 

 and fatty drops. 



And this is true not only of the 

 Tccnice, but of the majority of the 

 Bothriadae, whose embryos have notably 

 a similar form and armature. Only in 

 the embryos of Jlothriocephalus latus 

 do I find a greater differentiation, for 

 in this case there are not only distinct 

 fibrous bands, which are attached to 

 the roots of the hooks and move the 

 latter, but also four roundish groups of 

 cells embedded in the body, as will after- 

 wards be more particularly described. 



The embryos of the Bothriadre exhibit many other peculiarities 

 in addition to these, both in origin, differentiation, and mode of life. 



'urn 





FIG. 177. Ciliated embryo of 

 Bothriocephalus Latus. ( x 500.) 



