ZOOLOGY AND BOTANY, MICROSCOPY^ ETC. 343 



the characteristic cephalic process, but the simple oj-shaped eye-dot 

 was converted into two irregular black dots, while the internal 

 changes that were seen indicated a metamorphosis into the sporo- 

 cyst stage. 



When the embryo escapes from its shell it contains all its germ- 

 cells, which occupy the hinder portion of the body-cavity, while the 

 anterior half is filled with a granular mass, which may be looked 

 upon as the rudimentary enteron. At this stage the embryo has, in 

 its general structure, so striking a resemblance to the Orthonectida 

 of Giard, that the author is of opinion that these forms, just like the 

 Dicyemidae, must be regarded as of the Trematode group ; the fact 

 that they never pass beyond an embryonic condition, even although 

 they exhibit a complete differentiation of the sexes, need not cause 

 much astonishment, if we reflect that the sexually mature entozoa 

 of a large number of Invertebrates are, after all, to be morphologi- 

 cally referred to more or less developed larval forms ; in addition to 

 this, we may note that there is not really the difiference which there 

 is ordinarily supposed to be between the germ-cells of the Trematoda 

 and the female generative products. After swimming actively about 

 for some time, the embryo makes its way into a snail, and generally 

 into the respiratory cavity. As a rule, the ciliated investment is now 

 lost, and the two eyes become separated ; the form of the body 

 meanwhile ceases to be conical, and becomes more or less compressed. 

 The loss of the cilia is, of course, the expression of the commence- 

 ment of the parasitic life ; before it begins the animal makes some 

 powerful peristaltic movements, which loosen the cells. As soon as 

 the animal has completely entered into a resting-period, a thin layer 

 of clear cuticular substance is secreted around its outer surface ; this 

 forms a kind of cyst, which is perfectly adapted to the form and 

 changes in form of the body. Increase in size chiefly affects the 

 germinal cells, some of which rapidly, and others less rapidly, divide 

 repeatedly, and give rise to larger cell-aggregates ; this growth leads 

 to the enteron being pushed forwards, till it forms a kind of inner 

 cap for the cephalic end of the body, the eyes become altered in 

 position, and the number of the refractive granules increases. 



All the germinal cells, however, do not undergo division and 

 further development, a large number remain in their earlier con- 

 dition ; so again, during the first days of parasitic life, a number of 

 sporocysts die down ; some of those that become further developed 

 would seem to have the power of dividing ; at any rate the increase 

 in the size of these parasites is less an active than a passive pheno- 

 menon ; it is the consequence mei'ely of the regular growth of the 

 germ-spheres, which reacts on the form of the embryo ; the walls of 

 the body now become thicker, and lose largely their power of con- 

 tractility; the ciliated funnels would seem to disappear, and even 

 the eyes become obscured ; the last signs of the rudimentary enteron 

 are now also lost. Some of the germ-spheres contained within the 

 body begin to elongate, till they form tubes of some considerable size, 

 presenting a specific internal and external organization and forming 

 definite creatures. The inequality in the rate of development of the 



