413 



the germinal vesicle is seen to jjersist and divide, has been 

 recently observed by Haeckel in his studies on the develoj)- 

 nient of the Siphonophora. A parallel to the variability of 

 the ovum in the definition or non-definition of a nucleus is to 

 be found in the red corpuscles of some pyrensematous Verte- 

 brata. It is undeniable, as pointed out by Mr. Savory, that 

 generally no nucleus can be seen in the circulating red 

 corpuscles of the Frog. It is equally certain that often 

 under the same circumstances they are well defined — a con- 

 dition to be distinguished from that of granulation. 



A table giving a summary of the different modes of for- 

 mation of the blastoderm is given by Dr. Van Beneden, 

 which we extract. The thorough way in which he has gone 

 into his subject, and the importance of the views he advocates, 

 will render this book classical in embryogeny, whilst its 

 clear style, careful historical review, and interesting subject- 

 matter should induce every student to master its contents. 



(-Total 



LPartial 



fWithout separation of the 

 ! protoplasmand deutoplasm 



I fOccurringatthe 



{ I termination of 



the cleavage 



(' 



With sepa- 



ration 



At the com- | 

 mencementof-^ 

 the cleavage . 



L^ 



> Mammals. 



Gammarus locus- 

 ta, many Mol- 

 luscs, Nema- 

 |_ tods, etc. 

 ( Entoconcha mira- 

 I bills. 

 Heteropods, Pte- 

 ropods, Nephe- 

 lis. 

 Leptoplana Ire- 

 \ mellaris. 



fwithout separation at the f^'^'^f „ ^'f!?''' 

 I termination of cleavage of Bjrds.Reptiles, 

 the protoplasm from the J Plagiostoms 

 deutoplasm of the cica-l certain Crusta- 

 I tricula .... cea, iVe*a/^a, 

 I 1^ Mysis. 



I^With separation . . . Cephalopods. 



(-Separation of the protoplasm before fecundation | ^'o'"^/" j^ ^"'^ 



I J rimmediately after „ .\^%\ ^'*''*^"^' 



S ) I Caligus. 



•2 Separation after J T Arachnida, Asia- 



L fecundation .) f Progressively . < cus, Gamniari 



Later .■<, [ of fresh waters. 



Rapidly . . Insects. 



■^ 



VOL. X. NEW SER. 



E E 



