46 EMBRYOLOGY. 



others) that in other objects also, and in other branches of the animal kingdom, 

 the processes of fertilisation take place in essentially the same manner. At 

 the same time the comprehension of the processes of fertilisation was 

 essentially advanced, especially by the works of VAN BENEDEN on the egg 

 of Ascaris megalocephala, to which have been added the important investiga- 

 tions of BOVEEI and others on the same object. STEASBUEGEB has established 

 in a series of excellent researches the identity of the processes of fertilisation 

 in the animal and vegetable kingdoms. 



Finally, the phenomena of fertilisation were utilised simultaneously by 

 STEASBUEGEE and myself for the foundation of a theoiy of heredity, in our 

 endeavor to prove what others (KEBEE, HAECKEL, HASSE) had previously 

 expressed as a conjecture that the male and the female nuclear substances 

 are the bearers of the peculiarities which are transmitted from parent to 

 offspring. KOLLIKER, Roux, BAMBEKE, WEISMANN, VAN BENEDEN, BOVERI, 

 and others have since expressed themselves in a similar manner. 



SUMMARY. 



1. At maturation the germinative vesicle gradually rises to the 

 animal pole of the egg, and thereby undergoes a regressive meta- 

 morphosis (degeneration of the nuclear membrane and the fibrous 

 network, mingling of the nuclear fluid Kernsaft with the proto- 

 plasm). 



2. A nuclear spindle (polar spindle or direction-spindle) is de- 

 veloped out of remnants of the germinative vesicle, principally, 

 indeed, out of the substance of the germinative dot, which breaks 

 up into chromosomes. 



3. At the place where the spindle encounters the surface of the 

 yolk with one of its ends, there are formed two polar cells or direction- 

 bodies (Richtungskorper) by means of a process of budding, which is 

 repeated. 



4. At the second budding, half of the nuclear spindle remains in 

 the cortex of the yolk, and is metamorphosed into the egg-nucleus. 

 The egg is then ripe. 



5. In the case of eggs which develop parthenogenetically (Arthro- 

 poda), ordinarily only one polar cell is formed. 



6. At fertilisation only a single spermatozoon penetrates a sound 

 egg (formation of a cone d 'attraction, detachment of a vitelline mem- 

 brane). 



7. The head of the spermatozoon is converted into the spermatic 

 nucleus, around which the neighbouring protoplasmic particles are 

 radially arranged. 



8. Egg-nucleus and spermatic nucleus migrate toward each other, 

 and in rncfct instances immediately fuse to form the segmentation- 



