416 TRANSACTIOXS AND PROCEEDINGS OF [Sess. lvi. 



sperm- nucleus causes an intense radiation, analogous to that 

 observed during division. In advance of the radiation, the 

 sperm-nucleus travels towards the egg-nucleus, it reaches the 

 latter, unites with it, and forms, conjointly with the egg- 

 nucleus, a single nucleus, the division-nucleus (Furchungs- 

 kern), which latter soon develops into a nuclear spindle, 

 the division-spindle (Furchungs-spindel), and thus gives an 

 impulse to the commencement of embryonic development, 

 namely, to the division of the egg. As only now fecunda- 

 tion has been completed, we arrive at the fundamental 

 proposition, that the essence of fecundation consists in the 

 union of egg-nucleus and sperm-nucleus (Echinoderm). In 

 many instances an abbreviation of the process may occur, 

 inasmuch as the stage of the division-nucleus (Furchungs- 

 kern) is omitted, when the egg-nucleus and sperm-nucleus, 

 without previous union, proceed at once to the stage of the 

 nuclear-spindle (Furchungs-spindel), as in Ascaris" a fact 

 which had been worked out by v. Leneden and Boveri. 



Strasburger also considers fecundation to depend on a 

 union of the. sperm-nucleus with the egg-nucleus, and the 

 cell-substance (cytoplasm), not to share in the process, 



Guignard,* from a study of the process of fertilisation in 

 Lilium Martagon and Fritillaria, concludes that fertilisation 

 does not consist only in the fusion of the two nuclei of 

 different sexual origin, but also in the fusion of the cyto- 

 plasma of the two sexual cells, as he observed the coalescence 

 of the paranuclei (" directing spheres, or tinoleucites "). The 

 process is shortly this : — After the division of the repro- 

 ductive cell of the pollen-grain into two daughter-cells, the 

 anterior one of the two is provided with two tinoleucites in 

 front of the nucleus, while the egg has its two tinoleucites 

 above the nucleus. Thus the two pairs of tinoleucites are 

 brought in close contact with one another, they fuse, and 

 only two tinoleucites ai'e now seen in the Q^(f. The newly 

 formed pair of tinoleucites then separates, in order to allow 

 the nuclei to fuse. Later on the tinoleucites form the poles 

 of tlie zygote-nucleus, the latter divides, and induces a 

 division of tlie zygote. Thus fertilisation is completed. 



Sachs (I'hy.siology of Plants, p. 708) defines fertilisation 

 as the act Ijy which " something " is added to the substance 



* Cjinpte Kcnd., C. xii. (1891), pp. 132C-2. 



