William J. Moenkhaus 37 



in sections of such eggs. Figure 1 (Plate I) shows the three pronviclei 

 before their fusion. This egg would in all probability have fallen into 

 four cells at once. In the metaphase there are two spindles placed at 

 right angles to each other, an aster at each of their poles and at the 

 point of intersection the chromosomes are being distributed. I am un- 

 able to say whether in such dispermic eggs more than two spermatozoa 

 enter of which only two would then succeed in conjugating with the egg 

 pronucleus. 



Having such an easy way of producing dispermy I isolated large num- 

 bers of such eggs for further development to see whether I might be able 

 to obtain any evidence on the question of the relation of double impreg- 

 nation and double monsters or double embryos. Fol., 83, was the first 

 to raise this question in connection with his studies on Echinoderm 

 eggs. He obtained from a lot of polyspermic eggs a considerable num- 

 ber of double and multiple gastrulse. He maintained that the poly- 

 spermic condition was responsible for this result. In 1887 Oscar and 

 Eichard Hertwig reared many thousand polyspermic Echinoderm eggs 

 and obtained only about ten double gastrula^, a proportion entirely too 

 small to lend any support to the hypothesis of Fol. Further observa- 

 tions of Oscar Hertwig, 92, on isolated polyspermic frog eggs and of 

 Driesch, 93, on isolated dispermic Echinoderm eggs speak against this 

 hypothesis. In the dispermic fish eggs I hoped that the double char- 

 acter might show itself, in the first place, in the double grouping of the 

 cells in early cleavage and, in the second place, in the appearance of a 

 double embryonic shield which could be taken as an indication of an 

 attempt to produce two embryos. In regard to the first, it was found, 

 as already intimated, that the early cleavage stages, so far as the form 

 and grouping of the blasto meres are concerned, do not differ from the 

 normal eggs. In regard to the second, none of the eggs went beyond 

 the late cleavage stage. A careful search failed to reveal any sign of 

 even a beginning of an embryonic shield. Inasmuch as the majority 

 of the normally impregnated hybrid eggs develop far enough to form an 

 embryonic shield and many of them considerably beyond, the fact that 

 none of the dispermic eggs formed such shields must be taken as evi- 

 dence against the theory of any relation between dispermy and double 

 embryos. 



3. Later Development. — When cleavage has well progressed in the 

 Fimdulus hj'brid the blastoderm spreads and the germ ring with a faint 

 indication of an embryonic shield, forms. From this stage on a variety 



