114 LECTURE VI. 



in the one process the successive division of the germ-cells goes on 

 without a corresponding cleavage of the yolk, but this is penetrated 

 by the multiplying germ-cells, is absorbed, assimilated, and converted 

 into the matter of such germ-cells : in the other process the attractive 

 force of the germ-nuclei seems to be greater ; the whole yolk is divided 

 by the first bipartition of the original germ-cell, and is afterwards 

 assembled around these divisions, as they successively arise, as in Jigs. 

 52 — 56. The subdivisions of the yolk decrease in size as they aug- 

 ment in number, and the vitelline matter is at length, by the reiterated 

 processes of developement, liquefaction, and assimilation of nucleated 

 cells, sufficiently subdivided and refined, and each subdivision or cell, 

 by the concomitant partition of the clear spermatic nucleus or hya- 

 line, has become adequately vitalised or fertilised, so as to be ca- 

 pable of its further metamorphosis into the appropriate tissues of the 

 embryo worm. 



So far the process is essentially the same with that in all other ova 

 up to the mammal, and witliout doubt in man. The materials for the 

 future being are accumulated in a duly subdivided state, like the 

 bricks or hewn stones collected for the builder to operate on under 

 the guidance of the architect. With regard to the rough material for 

 formation of the Ascaris, a depression first appears on one side of the 

 minutely subdivided germ-mass, which, as this deepens, assumes the 

 form first of a cup, and then of a ring : the space so formed between the 

 germ-mass and the chorion becomes filled by a clear fluid. The ring 

 next presents a constriction at one point, which divides and transforms 

 it into a cylinder with two equal obtuse ends in apposition {Jig. 57.). 

 By the lengthening and attenuation of the cylindrical mass, the ends 

 overlap and the ring assumes the character of a coil {Jig. 58.) ; and 

 now something like an integument, containing a fine granular tissue, 

 may be discerned. Further elongation and attenuation produce one or 

 two spiral coils, and a greater clearness of the tissues of the embryo 

 worm makes its character plainly manifest {Jig. 59.). In the Ascaris 

 at this period the characteristic three-lobed mouth may be discerned ; 

 and soon after the alimentary canal can be distinguished from the 

 integument, both having been formed by the subdivision and meta- 

 morphosis of the primitive cells. The young animal, thus built up, 

 now begins to move briskly within the egg-membrane, assimilates the 

 remaining vitelline mass, and is soon strong enough to burst its prison, 

 and commence its independent career of existence. 



The Entozoa are hardly less remarkable for their tenacity of life 

 and revival from a state of apparent death than the Infusoria, and the 

 knowledge of this property is indispensable to a fair estimation of the 

 chances of the re-introduction of the ova of Entozoa into the bodies 



