144 SYDNEY J. HIOKSON. 



Tochter kernplatten stets so fort weit aus eiuander riicken." 

 Henking (21), too, was unable to find the first division of the 

 oosperm nucleus of Musca. 



Now, in Musca, and in many other insects in which the early 

 divisions of the oosperm nucleus have not been made out, the 

 occurrence " of free nuclear formation " has been described in 

 the young embryo. Whence come these free nuclei? It can 

 hardly be believed that they are actually formed in the cell 

 substance from something that is not directly derived from a 

 pre-existing nucleus. All the evidence of modern histology 

 tends to prove that nuclei are derived from nuclei, and nuclei 

 only, and it is only reasonable to suppose that the so-called 

 "free nuclei" of insect embryos are formed by the growth or 

 fusion of fragments of the oosperm nucleus. 



The evidence in support of this hypothesis is not the purely 

 negative evidence of the absence of any direct proof of mitotic 

 division of the first nuclei, but the fusion of minute chromatin 

 bodies to form larger ones has actually been observed by 

 Henking (23) in the embryos of Pieris, Pyrrochoris, and Lasius. 



But it is extremely probable that fragmentation of the 

 oosperm nucleus is of very frequent occurrence in the eggs of 

 insects. In many cases, both in large yolk-laden eggs and in 

 small yolk-free eggs, the fertilisation is followed by the 

 appearance of numerous nuclei in the substance of the egg. 



In Neophalax concinnus, one of the Phryganids, the 

 division of the oosperm nucleus was not observed by Patten 

 (46), and the following is his account of the early stages: — 

 " Within ten or twelve hours after oviposition — the time 

 varying with the temperature — a clear space makes its ap- 

 pearance at the surface of the egg, and gradually increases 

 until it has attained the breadth of the future blastoderm. 

 In this layer, which has been called the 'blastema,' the pro- 

 toplasm has, under ordinary conditions, a very homogeneous 

 appearance, with occasionally lighter, less refractive spots, 

 which appear like vacuoles, but in which, when observed more 

 closely and under slight pressure of a cover-glass, or especially 

 when treated with a very little acetic acid, faintly marked 



