394 Dr. C. F. Liitken on Spontaneous 



we possess interesting observations by Mr. Macintosh, showing 

 that certain Nemertina (Borlasia) when in confinement may- 

 break up into a quantity of fragments, all of which possess 

 the power of regeneration so as to become complete individuals. 

 This kind of division, which is neither entirely spontaneous 

 nor entirely artificial, is difficult to range under any definite 

 scientific determination ; we find analogous cases among the 

 Actiniae. 



Spontaneous division (schizogony) seems therefore to occur 

 principally in two great groups of the lower animals : — the 

 Protozoa (Monera and Rhizopoda) , which are reduced to simple 

 cells, and which consequently may be divided artificially and 

 divide themselves ; and the Radiata (Echinoderms and Coelen- 

 terata), in which the divisibility is partly connected in a 

 perfectly natural manner with the radiate structure. But both 

 in the Echinodermata and in the Coelenterata spontaneous 

 division is at the same time intimately connected with regen- 

 eration, upon which it depends, and from which it cannot be 

 separated : we may regard it as the most perfect expression of 

 its development ; and in some Coelenterata (especially the 

 Actiniae) it is moreover in intimate connexion with gemmation 

 (blastogony) , and passes so insensibly into perfectly cha- 

 racterized phenomena of gemmation, that, at any rate in a 

 great many cases, it seems impossible to trace a boundary 

 between these two modes of reproduction, which seem to be so 

 essentially different. As the experiments made upon this 

 subject have never been considered in their totality, and it 

 would be very desirable that they should be resumed in a 

 methodical manner, I have appended to my communications 

 on spontaneous division in the Echinodermata a short statement 

 of what has been ascertained as to regeneration and artificial 

 and natural division in the Medusae and Actiniae. By this 

 means I propose to collect some materials which may assist in 

 answering the following questions : — Of what facts which may 

 throw light upon the spontaneous division of certain Radiata 

 is science in possession ? and in what relation does spontaneous 

 division stand on the one hand to artificial division, and on the 

 other to gemmation and other forms of agamic reproduction ? 



With regard to the Medusae, I leave on one side the so-called 

 scissiparous division of the Scyphistoma, and also pass over in 

 silence the celebrated observations on the spontaneous and 

 artificial division of the freshwater polypes, as likewise the in- 

 teresting experiments of M. Hackel on the artificial division 

 of the ova and embryos of the Siphonophora. In fact, in all 

 these cases, as in the researches of Dalyell and Reid on arti- 

 ficial division (both longitudinal and transverse) in the Scyph'- 



