OF PLANOCERA ELLIPTICA. 317 



either forwards or backwards in a vertical plane.* The embryo, therefore, is abso- 

 lutely free, and can assume any position and turn in any direction. For, the direction 

 itself may change almost instantly, that is to say, if an embryo moves now from 

 right to left, the next moment it may move from left to right. I have repeatedly 

 seen a vitelline sphere, artificially pressed out of its external envelope, continue to 

 move as if still enclosed. When crushed to the isolation of the constituent cells, all 

 of these, large and small, began to dance, turn, whirl independently of each other, 

 as if controlled by an irresistible impulse of their own. 



Another phenomenon which illustrates the independence of the cells, took place 

 under my eyes. An embryonic sphere, vi^hile in motion, lost about one third of its sub- 

 stance, the cells of which became loose within the albuminous zone, and were carried 

 by the current, around the remaining portion of the original vitelline sphere. These 

 loose cells, after a while, congregated into a small sphere, and for a moment one would 

 have thought that there were originally two embryos in the same egg, a large and 

 a small one. Soon, however, the small sphere was destroyed by the other and its 

 cells again loosened, when it rebuilded itself once more. But now it became a per- 

 manent little sphere, which, in its motion within the same area as the large one, 

 caused many irregularities and perturbations, in the general movements of the latter. 



We have here one of the most attractive and wonderful phenomenon which nature 

 may display ; a phenomenon hidden from the eye of the great multitude of men. How 

 many are there, who, at a glance into that sanctuary, would feel powerfully impressed 

 with the thought that a divine mind, an allwise Creator is the author of the small as 

 well as of the great in the whole universe. A moment of simple reflection would 

 convince them that such an activity like that which they thus behold, in a little 

 sphere of organic substance, cannot be accounted for by the mere attributes of mate- 

 rial forces. 



^ 3. About twelve hours after the motion has begun, the embryonic mass, still 

 circular in general form, assumes now two aspects in its substance : 1st. The central 

 part, which is composed of large cells either transparent or semi-transparent, contain- 

 ing a milky fluid at divers degrees of development (fig. 55, a. b.c.) ; and 2d, the 

 peripheric layer, composed of ordinary vitelline cells from the surface of which vibrillae 

 will grow (fig. 56). 



^ 4. The embryonic mass, after a lapse of another twelve hours, acquires a plastic 

 elasticity by which the primitive spherical form is subjected to the most diversified 

 though temporary variations. This fact is another evidence that cells may contract as 

 well as muscular tissues, although the physiology of this function is not easily explain- 

 ed in the actual state of our knowledge on this subject.f 



§ 5. The transformation of the spherical embryo into a symmetrical animal is effec- 



*The horizontal and vertical planes arc here spoken of with reference to the observer's orientation. 

 1 1 allude to the corttaction of cells in jelly fishes (Medusje) observed by Prof. Agansir. 



80 



