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brought forAvard some most interesting facts to establish its 

 truth. The work consists of historical introduction, remarks 

 on the fundamental form and topography of the Siphonophora 

 larvae, individual development of Physophora, varieties and 

 monstrosities of PJujsophora larvse, systematic remarks on the 

 new Algamidean genus Crystallodes, individual development 

 of CrystaUodes, experiments on the multiplication of Crystal- 

 lodes larva3 by artificial division, varieties and monstrosities 

 of Crystallodes larvae ; individual development of Athorybia, 

 reflections on the individual development of the Siphonophora 

 and on the signification of this in the elucidation of their 

 palseontological development. The plates illustrating the 

 work are admirable, and are, as Professor Haeckel observed 

 to us, among the best executed which he has ever had done. 

 Among the more general points of interest in this very im- 

 portant memoir, we will here jooint ovit a few. The cells 

 which result from the yelk cleavage exhibit amoebiform move- 

 ments, as has been observed in the eggs of fish and batrachia. 

 It is important to note that the single egg cell divides itself 

 into two, as observed in some Molluscs, Insects, and recently 

 by Dr. Van Beneden in Trematod worms, this being the first 

 stage of yelk division. How this is to be reconciled with the 

 total disappearance of the germinal vesicle in Vertebrate ova, 

 and in those of Annelids after fecundation and before yelk 

 division has become apparent, is a matter of considerable 

 importance. The amoebiform processes to which the cells 

 give rise become cilia, thus establishii:ig a connection between 

 these two kinds of processes. In some of the young forms 

 described and figured, Haeckel recognises a rudimentary 

 representative of the axial canal of the hydroid polyp which 

 he supposes appeared as one of the developmental phases of 

 the ancestors of the Siphonophora. Physophora developes 

 directly by conversion of the whole yelk mass, being in fact 

 holoblastic. Crystallodes, on the other hand, buds off from 

 the primitive yelk bag so as to develop an embryo and 

 attached yelk bag, being meroblastic ; the two genera are at 

 the same time closely related as members of the Siphonophora. 

 Professor Haeckel made some very curious experiments with 

 Crystallodes, cutting the young ovum just after yelk division 

 into two, three, four, or even five pieces. Each part thus 

 cut off" continued to develop, but varied in the extent of 

 its subsequent development according to the degree of divi- 

 sion which had been practised. These observations are really 

 worthy of most earnest attention from all physiologists ; they 

 seem to demonstrate that the earliest formed cells of the orga- 

 nism have a common potential as well as an undifferentiated 



