STflUCTUEE OF THE FREE-SWIMMING EMBRYO. 



725 



Fig. 387. — Free-swimming embryo of 

 Bothriocephalus latus with the protoplas- 

 mic threads between the body and the 

 ciliated mantle. (After Schauinsland.) 



the embryos to the presence of protoplasmic threads, which extend in 

 regular order between the two lamellse, and thereby simulate cells. 

 Just as the two lamellse of the mantle 

 are connected with one another by 

 threads, so, too, do threads connect 

 the embryo with the mantle, but the 

 latter are considerably fewer in 

 number and less strongly developed 

 (Schauinsland). They are best seen 

 in embryos which have lived for 

 some length of time in the water, 

 and in which the space below the 

 mantle has been enlarged by the 

 absorption of water. In the in- 

 terior of the embryonic body, which 

 has a diameter of 0'045 mm., and is 

 thus considerably larger than that of 

 the human bladder- worm, one recog- 

 nises in successful preparations not 



merely the fibrous strands which are inserted on the roots of the hooks 

 and move the latter, but also a tissue of very vesicular ceUs, which is 

 surrounded on all sides by smaller cells, and occupies especially the 

 bookless half. This does not consist, however, of a simple connected 

 mass, but is divided into four adjacent balls by the fibres and cortical 

 cells which insinuate themselves into it. The hooks themselves are 

 strongly developed (O'OIS mm. in length), and provided at the ends 

 with a sharply defined sickle-like claw, 0'006 mm. 



The longer the embryo lives freely, and the more the mantle 

 becomes inflated, the more do the em- 

 bedded granules disappear. In the same 

 way, the activity of the cilia decreases 

 and the motion becomes slower. At last 

 the embryo sinks to the ground. The 

 ciliary activity ceases, but the move- 

 ments of the hooks and the contractions 

 of the body may still be observed for 

 some time. In many cases, however, the 

 mantle has already been stripped off, so 

 that the embryo is now completely free, 

 and moves about with lively movements 

 of the hooks and of the body. It not un- 

 frequently happens that while the embryo 



is escaping, only the ex.ternal lamella of the mantle is rent, and in 

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Fig. 388.— Embryo of Bothrio- 

 cephalus latus escaping from its 

 ciliated envelope. 



