316 POLYEMBKYONY AND THE DETERMINATION OF SEX. 



the egg, but in a slower manner, and it is only when the embryo is 

 formed that it emits a ventral stolon; it afterwards divides trans- 

 versely into four buds, each one of which develops into a new indi- 

 vidual (according to Huxley, Kovalevsky, Seelinger, etc.). 



From the cases above cited, where the budding is effected in the 

 egg, one passes on insensibly to the very frequent and well-known 

 processes in which agamic reproduction takes place after the animal 

 has already left the egg (Coelenterata, Orthonectids, Dicyemids, 

 Plathelmintha, Tunica ta). The preceding observations appear, 

 therefore, to establish a continuous series linking the polyembrvony 

 of the Hymenoptera with the cases of agamogenesis that occur in 

 the advanced stages of development. 



Again, from a very general point of view, the processes of poly- 

 embryony ma}" be associated with the cases of experimental blas- 

 totomy recently recorded by several authors. 



Driesch {1892), causing a temperature of 31° to act on the eggs 

 of Echinids, obtained a separation of the blastomeres into two or 

 more groups; Loeb (1893) obtained a like result by mixing equal 

 parts of distilled water with the sea Avater in which the eggs are 

 found." 



Another experiment carried out by Loeb ( 1894) with the eggs of 

 sea urchins and by Bataillon (1900) with the eggs of Petromyzon 

 and of Teleosteans consisted in dividing the egg into several groups 

 of blastomeres bj^ means of a hot needle. Both of them obtained 

 complete larvae, each blast omere or group of blastomeres again con- 

 stituting an embryo by itself. 



Ryder (1893) obtained double monsters by shaking the eggs of 

 the trout. The vitellus accumulates on the U\o sides of the egg, 

 forming two distinct individuals. 



In the same way it is possible, by making a constriction around the 

 egg of Triton with a silk thread, to produce two complete larvae, 

 united only by the skin of the abdomen. (Endres, 1895; Speman, 

 1900 and 1901^ 



These investigations speak, as one sees, in favor of the so-called 

 hotrofic constitution of the egg, each blastomere or group of blas- 

 tomeres isolated in the manner indicated being capable of forming a 

 complete individual. 



Marchal expresses the facts very well in saying that as much in 

 spontaneous polyembryony as in experimental blastotomy each part 

 of the egg contains the complete hereditary patrimony capable of 



a The egg in absorbing the water bursts its membrane ; a portion of the 

 cytoplasm issues from the mouth of the rupture and forms a gross hernia, 

 which the author calls extraovat. The nucleus divides and sends forth a 

 young nucleus into the extraovat. In this manner, lilce the Intruorat, it develops 

 into a complete larva (after Delage, L'heredite, 1895, p. ;5.31). 



