MATURATION OF THE EGG, AND PROCESS OF FERTILISATION. 4& 



one injures the egg-cell. This may be accomplished either by 

 exposing it temporarily to a lower or a higher temperature, and 

 thus producing cold-rigor or heat-rigor, or by aft'ecting it with 

 chemical reagents, — chloroforming it, or treating it with morphine, 

 strychnine, nicotine, quinine, etc., — or by doing violence to it in a 

 mechanical way, such as shaking it. It is interesting to observe how, 

 with all of these means, the degree of superfetation is, to a certain 

 extent, proportional to the degree of the injury ; how, for example, a 

 small number of spermatozoa penetrate into eggs which have been 

 slightly affected with chloral, whereas a greater number penetrate 

 those which have been more strongly narcotised. 



In all unfertilised eggs the whole course of development becomes, 

 abnormal. But whether, as claimed in Fol's hypothesis, the origin 

 of double and of multiple organisms is referable respectively to the 

 penetration of two and many spermatozoa, must still be regarded as 

 doubtful. Certainly the question suggested richly deserves to be still 

 more thoroughly tested experimentally. 



History. — The facts here given concerning the theory of fecundation are 

 acquisitions of very recent times. To omit the older hypotheses, it was 

 generally assumed up to the year 1875 that the spermatozoa penetrate in great, 

 numbers into the substance of the egg, but that they there lose their activity 

 and become dissolved in the yolk. 



I succeeded in my study of the eggs of Toxopneustes lividus in finding- 

 an object in which all the internal phenomena of fertilisation may be 

 determined with ease and certainty, and in establishing (1) that in consequence 

 of fertilisation the head of a spermatic filament surrounded by a stellate figure 

 makes its appearance in the cortex of the yolk, and is metamorphosed into a 

 small corpuscle, which I called spermatic nucleus : (2) that within ten minutes- 

 egg-nucleus and spermatic nucleus copulate ; (3) that normally fertilisation is 

 accomplished by only a single spermatic filament, whereas in pathologically 

 altared eggs several spermatozoa may penetrate. I was therefore able at that 

 time to announce the proposition, that fertilisation depends upon the fusion of 

 two sexually differentiated cell-nuclei. 



A few months later, van Bbnbden announced that in the case of Mammal* 

 the segmentation-nucleus arises from the fusion of two nuclei, — as had 

 previously been observed by Aueebach and BOtschli in the case of numerous, 

 other objects, — and expressed the conjecture that one of them, which has at 

 first a peripheral position, might in part result from the substance of the 

 spermatozoa, which, in great numbers, as he maintained, fuse and become 

 commingled with the cortical portion of the yolk. An advance was soon after 

 this made by Fol, who investigated with the greatest detail the eggs of 

 Echinoderms at the very moment of the penetration of a spermatic filament 

 into the egg, and discovered the formation of a cone of attraction. .Since, 

 then it has been established by means of numerous researches (those of 

 Selenka, Fol, Heetwig, Calbbrla, Kupffeb, Nussbatjm, van Beneden,. 

 Ebebth, Flemming, Zachahias, Bovbri, Platner, Tafani, Bohm, and 



