gS PROBLEMS OF FERTILIZATION 



extremely active, they are apparently unco-ordinated, 

 so that the aggregation reaction is not given. 



As a general principle the rate of activity of sper- 

 matozoa is a function of the temperature, like other 

 biological processes, and the temperature range varies 

 with the species. 



2 . Contact 



All kinds of spermatozoa studied exhibit contact 

 reactions. Dewitz (1885, 1886) appears to have been 

 the first to study this subject; he showed that the 

 spermatozoa of the cockroach maintain contact with 

 sohd bodies and free surfaces of liquids; he studied 

 their thigmotactic rotations on the surface of the egg, 

 which finally result in the penetration of the micropyle 

 of this hard-shelled ^gg. In a drop beneath a raised 

 cover slip they divide in two groups, one in contact 

 with the floor, the other with the roof of the inclosed 

 space, and are absent in between. They are in constant 

 motion, describing circles of varying diameters always in 

 the same sense (anticlockwise), with reference to the 

 surface of contact; but these two groups appear to 

 revolve in opposite directions under the microscope, 

 owing to the direction of observation. 



Massart (1888, 1889) studied the reactions of the 

 spermatozoa of the frog and showed that in a drop be- 

 neath a raised cover slip they also divide in two actively 

 rotating groups, one in contact with the shde below and 

 the other with the cover slip above; similarly in a 

 hanging drop they accumulate in contact with the 

 glass above and the free surface of the drop below. 

 Buller (1902) states that when sea urchin spermatozoa 

 *'come in contact with a surface they either become 



