322 THE ANATOMY OF CESTODES. 



place in these eggs, for they have become large and generally round 

 balls with a more or less firm shell, which contains a clear globule, 

 with six slightly bent hooks (Fig. 173) arranged in pairs anteriorly 

 and laterally. These bodies are the embryos, first accurately observed 

 and described by v. Siebold. 



During the growth of the- joint in the Tcenice, the embryonic 

 development also progresses. The older mature joints, whose uterus 

 often appears of a rusty-brown colour from the contained eggs, have 

 gradually become pregnant animals. 



The size of the embryos of Tcenia and of their hooks varies greatly 

 in the difi'erent species. This is especially true of the hooks, which 

 often attain a disproportionate development, and 

 become so long that they penetrate the greater 

 part of the embryonic body. And even in the 

 same embryo there may be differences in the 

 degree and manner of their curvature. In 

 general, however, the structure of the hooks has 

 Fig. 174. — Embryonal ^ gj-eat resemblance to that of the adult Tcenix, 



booklet of Tcsnta cratenfor- ° ■ 



mis, from a bird. A, a except that as the root has a very straight 

 middle booklet ; B and c, course, the general form is more linear. 



anterior and posterior book- ^ t m c i ■ i 



lets. ( X 700, after v. Sie- In some species, such as the Tcenice of bnds, 

 ^'^^^) these hooks often exhibit a distinct motion. 



They approach with their free points a common apex, and in their 

 motion from it diverge downwards, the two side pairs moving almost 

 simultaneously in the lateral plane, and the middle pair somewhat 

 later in a median direction. 



The shell which surrounds these embryos, without, however, lying 

 closely upon them, is sometimes thin and smooth, and is sometimes 

 also furnished with granules or with a number of little perpendicular 

 rods close beside each other, as is especially the case in the larger 

 Cystotcenice (Fig. 173, A). Nor is this always the only covering of 



the embryos. In many species a 

 second and occasionally even a third 

 skin has been found, both of pecuhar 

 and striking form.^ But even in 

 cases where these extra coverings 

 around the shell are wanting, as in 

 T. i,f T. cm- the larger Tcenice of man and car- 



Fio. 175. — Egg of Tamta nana oo- . ° 



ourring in man, A ; and of T. solium, nivorous mammals. One sometimes 

 B, with shell and yolk skin. ( x 400.) noticcs, especially if the egg be cau- 

 tiously emptied, an albuminous envelope bordered by membrane. 



^ In this connection see the statements of v. Siebold regarding the egg-shell and form 

 of the eggs in the Twnim in Burdaoh's " Physiologie," 2 Aufl., Bd. ii., p. 203, 1828-35. 



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