AND THE LOWER ANIMALS. 19 



pulsion of the globules is followed in the mammal, as 

 in Hermella and Teredo, by a short period of repose. 

 The germ recovers its spherical form which had been 

 momentarily lost, and exhibits an entirely homogeneous 

 structure ; then the motion of the granules recom- 

 mences, this time affecting both the internal and 

 external portions. A ring-like constriction takes 

 place about the middle of the vital sphere and deepens 

 rapidly.* A second constriction then crosses the first 

 at right angles ; and this is followed by several others. 

 As the grooves increase in number, the entire mass 

 appears composed of hundreds of adherent vesicles, 

 which give it rather the aspect of a raspberry; but 

 the progressive multiplication of these vesicles gra- 

 dually renders the surface smooth, and brings it 

 almost to the original condition. The germ becomes 

 transparent, and its outer layers begin to present the 

 features of young tissue. These strange phenomena 

 are also common to all animals. f Discovered in the 

 frog by Messrs. Prevost and Dumas, they were soon 

 observed in a great number of invertebrata ; then in 

 fish, by Rusconi; in mammals, by Bischoff; and 

 finally in birds and scaly reptiles, by M. Coste.J At 



* According to M. Ch. Robin, the first groove makes its appear- 

 ance at the point from which the transparent globule has escaped, 

 and on this account he terms the latter the polar globule. But 

 this generalization is, to say the least, premature. 



t M. Ch. Robin states that the diptera of which we have 

 spoken are an exception to this rule. M. Lacaze du Thiers has 

 informed me of a similar state of things which he has seen in other 

 groups, but he wishes to confirm his observations by further inves- 

 tigations before giving them publicity. 



X M. Coste has shown that, in birds, scaly reptiles, and cartila- 

 ginous fishes, the segmentation in the neighbourhood of the little 



c 2 



