FERTILISATION x 



" Although it be a known thing subscribed by all, that the fostus assumes 

 its origin and birth from the male and female, and consequently that the egge 

 is produced by the cock and henne, and the chicken out of the egge, yet neither 

 the schools of physicians nor Aristotle's discerning brain have disclosed the 

 manner how the cock and its seed doth mint and coine the chicken out of the 

 egge." HARVEY. 



ALTHOUGH much progress has been effected, and many new facts 

 have been discovered, since Harvey wrote his famous dissertation 

 on " The Efficient Cause of the Chicken," the actual nature of the 

 process whereby the ovum, after being discharged from the ovary, 

 is endowed with a new vitality through union with a sper- 

 matozoon, is a problem the solution of which is still far from 

 complete. 



In 184:3 Martin Barry,' 2 as already mentioned, first observed the 

 union of the spermatozoon and ovum in the rabbit, and a little later 

 Newport 3 recorded its occurrence in the frog ; but it was not until 

 the last quarter of the nineteenth century that the significance of 

 the process was realised. It was largely through the work of 

 Hertwig, Strasburger, and van Beneden that most biologists came 

 to believe that the union of the nuclei of the gametes was the 

 essential act in the process of conjugation. The more recent 

 investigations of Boveri and others do not, however, entirely support 

 this conclusion. 



As already described, the head of the spermatozoon represents 

 the nucleus, and contains the chromatin material. When the sperm 

 penetrates into the substance of the ovum the tail becomes absorbed, 

 but the head remains as the male pronucleus. The matured nucleus 

 of the ovum, or female pronucleus (the two polar bodies having 

 been discharged), passes towards the centre of the cell, where it 

 unites with the male pronucleus which generally becomes somewhat 

 enlarged. The middle-piece of the spermatozoon also enters the egg, 



1 Revised, with numerous additions, by Cresswell Shearer. 



2 Barry, "Spermatozoa Observed within the Mammiferous Ovum," Phil. 

 Trans., 1843. 



3 Newport, "On the Impregnation of the Ovum in the Amphibia," Phil. 

 Trans., 1851. 



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