FERTILISATION OF THE EGGS OF AMIMALS. 163 



with freshly obtained spermatozoa be made as quickly as 

 possible aud examined at once^ one notices that a large 

 number of spermatozoa are already rotating in the manner 

 just described upon the upper and lower surfaces. 

 One also notices, however, that a considerable number 

 of spermatozoa have become attached by the ends of 

 their conical heads. The heads then generallj^ continue to 

 move about their tips, usually executing circles apparently 

 either clockwise or counter-clockwise. 



If a single spermatozoon not fixed by the head and rotating 

 in circles upon glass be watched, it will often be seen to make a 

 number of consecutive revolutions and then suddenly stop in its 

 course and become fixed to the glass by the point of its head. 

 In this way the number of spermatozoa attached to the glass 

 surfaces gradually increases. 



Although the spermatozoa of the Echinoidea appear to 

 become most easily fixed to surfaces by the tips of their 

 conical heads, yet fixation may take place in several other 

 ways. Thus, I have seen spermatozoa attached (1) by the 

 middle of the side of the head, (2) by the middle-piece, 

 proof of such fixation being rotation of the head around 

 these respective parts. The spermatozoa can also become 

 attached by the hinder half of the tail, for I have observed 

 cases in which the head and fore part of the tail have made 

 excursions from the glass, returning, however, to their 

 original position, while the hind part of the tail remained in 

 one place, immovable upon the glass surface. In yet other 

 cases one sees a spermatozoon apparently attached to the 

 glass by its whole length, slight waves of movement pro- 

 ceeding down the tail from just below the head. When 

 spermatozoa have entirely come to rest upon a surface they 

 are very frequently seen to be attached to the glass by their 

 whole length, a fact which Ballowitz^ has also observed in the 

 case of the spermatozoa of Insects. From these various 

 observations it appears that a spermatozoon may become 

 attached to a surface in almost every possible manner. 

 ' Ballowitz, loc. cit., p. 393, footnote. 



