244 RAMBLES OF A NATURALIST. 



yolk is formed of very minute opaque granules, united 

 together by a perfectly diaphanous matrix. 



If we throw one of these eggs into sea-water, in 

 which some of the male organic corpuscles are mov- 

 ing, we shall see, after a few moments' immersion, 

 that it has become the seat of a condition of vital 

 activity which may be easily watched through the 

 microscope. A mysterious force seems to mould 

 these elements, blending them together on all sides. 



The yolk presents alternating movements of con- 

 traction and expansion ; the spot and the vesicle suc- 

 cessively disappear; a transparent globule escapes 

 from the midst of the vitellus, and then begins the 

 singular phenomenon discovered by MM. Prevost 

 and Dumas.* A circular streak is observable round 

 the vitellus, which divides spontaneously first into 

 two, and then into four parts, and goes on subdivid- 

 ing thus successively, until it is only composed of 

 very minute globules. In proportion as this cleavage 

 progresses, the granular character of the vitellus 

 diminishes, and finally disappears. The entire mass 

 assumes the appearance of young tissues. At this 

 period, we soon begin to perceive a few small fila- 

 ments, which are at first immoveable, but speedily 

 begin to strike the liquid with jerking motion. 

 These filaments become more and more multiplied 

 when the young Hermella after having balanced 

 itself for some time, as if to try its nascent organs, 

 suddenly leaves the solid plane which supported it 



* The cleavage of the vitellus, which was originally discovered 

 by physiologists in the egg of the frog, has since been observed in 

 all animals that have been investigated under favourable conditions. 



