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SCIENCE. 



[N. S. Vol. XXIV. No. ()25. 



develop into a new individual (according to 

 Huxley, Kovalevsky, Seelicer, etc.). 



From the cases mentioned, where the bud- 

 ding takes place in the egg, one passes insen- 

 sibly to more frequent and better-known phe- 

 nomena in which agamic reproduction takes 

 place after the individual has already issued 

 from the egg (as in the Coelenterates, Ortho- 

 nectidae, Dicyemidse, Platyhelminths, Tuni- 

 cates). The preceding observations seem 

 then to establish a continuous series connect- 

 ing the polyembryony of Hymenoptera with 

 the cases of agamogenesis occurring in ad- 

 vanced stages of development. 



In general the facts of polyembryony may 

 be also said to approach the cases of experi- 

 mental blastotomy recently observed by vari- 

 ous authors. 



Dreisch (1892), passing a temperature of 

 31° over the eggs of echinids, obtained a sepa- 

 ration of the blastomeres into two or more 

 groups; and Loeb (1893), by mixing distilled 

 water in equal parts with the sea-water in 

 which the eggs were found, produced the same 

 result. 



Another experiment of Loeb, 1894, upon the 

 eggs of Echinus, and by Bataillon, 1900, upon 

 the eggs of Petromyzon and of teleosts, con- 

 sists in dissociating the egg into several groups 

 of blastomeres by means of a heated needle. 

 Both obtained complete larvae, each blastomere 

 or group of blastomeres forming an embryo. 



Ryder in 1893 obtained double monsters by 

 the shaking of the eggs of trout. The vitellus 

 forming on both sides of the egg made two 

 distinct individuals. 



One can even make two complete larvae of 

 Triton united only by the skin of the ab- 

 domen, by constricting the egg with a silken 

 thread (Endres 1895, Speman 1900 and 1901). 



These facts favor, it may be seen, what is 

 called the isotropic condition of the egg, each 

 blastomere or group of blastomeres isolated by 

 one of the methods indicated being capable of 

 forming a complete individual. 



Marchal expresses this very well in saying 

 that both in spontaneous polyembryony and in 

 experimental blastotomy each part of the egg 

 contains the complete hereditary patrimony 



capable of ending in the formation of an in- 

 dividual conforming to the specific type. 



In the papers of Marchal and Bugnion no 

 reference is made to the recent very important 

 work of Professor Conklin in which he shows 

 that the eggs of the Ascidians, Cynthia partita 

 and Oiona intestinalis, are not isotropic and 

 that the cytoplasm of the egg is not equipo- 

 tential. Dr. Conklin concludes that " Experi- 

 ments which demonstrate the totipotence of 

 blastomeres or regions of the egg prove noth- 

 ing with regard to the presence or absence of 

 differentiation in these parts. Some eggs 

 with a high degree of differentiation have at 

 the same time great capacity for regulation." 

 Workers in this field must reckon with these 

 important results. 



Another question which presents itself is 

 that of knowing whether among insects poly- 

 embryony ought to be considered as having 

 preceded or followed phylogenetically the 

 other methods of agamic reproduction such as 

 paedogenesis among the Cecidomyiidae or cyc- 

 lical parthenogenesis among the Aphididae 

 and the Cynipidae. Harmer, for the Bryozoa, 

 arrived at the conclusion that embryonic scis- 

 sion is a consequence of the blastogenetic fac- 

 ulty of the adults. Perrier extends the same 

 point of view to all budding animals. 



Considered from this point of view, the 

 polyembryony of the Chalcididae appears not 

 as an initial phenomenon, but as a secondary 

 adaptation due to an acceleration of embryo- 

 genetic process (tachygenesis of Perrier, 

 1902). The result of this adaptation is, con- 

 sidering the short and precarious existence of 

 the adult Encyrtus, to assist in the preserva- 

 tion of the species by pushing its multiplica- 

 tion to the highest possible degree. 



As to the determining cause of the division 

 of germ, Marchal thinks that it is from the 

 sudden surrounding with more dilute liquids 

 in the interior of the nourishing mass and in 

 a concomitant modification of the osmotic ex- 

 changes in the interior of the cellules. One 

 sees, in fact, with Encyrtus that polyembry- 

 ony reaches its greatest intensity at the mo- 

 ment when the larva of the Hyponomeuta 

 commences to feed (in the early days of 

 April), and for the Polygnotus at the period 



