150 A. H. REGINALD BULLER. 



find their way to and tlirough the micropyles of the eggs 

 owing to the remarkable fact that on coming to a surface 

 they remain in contact with it and continue to move in circles. 

 This characteristic, which will be discussed more fully after- 

 wards^ I have found also shared by the spermatozoa of repre- 

 sentatives of every group of the Echinodermata. 



Massart^ made a careful investigation of the fertilisation of 

 fi'ogs' eggs. He came to the conclusion that the spermatozoa 

 come in contact with the gelatinous coat by accident, and 

 cling to it owing to a special sensibility to contact. He found 

 that they bore through it radially. He believed that this is 

 explained on the supposition that the spermatozoa seek to 

 bore from the more watery outer layers to the less watery 

 inner layers in consequence of a sensibility to the differences 

 of saturation. 



My own investigations^ undertaken at Naples^ were made 

 to determine the nature of the forces which bring tlie 

 spermatozoa and eggs of the Echinoidea in contact, especial 

 attention being paid to the chemotactic question. The work 

 was taken up after a fairly extended study of the chemotaxis^ 

 of the spermatozoa of ferns. 



II. Some Fertilisation Problems. 



In the case of such eggs as those of the Echinoidea, which 

 are surrounded by a thick gelatinous coat^ some of the 

 ])hysiological questions that may be asked in regard to the 

 manner in which the spermatozoa meet and fuse with tln'm 

 are as follows : 



1. Does a spermatozoon meet the gelatinous coat (zona 

 pellucida) by accident, or is it attracted to it b}' some 



' Massait, (1) '"Sui- rirrilal)ilit6 des SpeniuilozniMcs dv. la (Jniioiiilk',"' 

 ' Bull. (Ic I'Acad. roy. dc lkl-;ifiuc,' 3m(; t.cr., t. xv, No. 5, 1SS8 ; (2) " Sur la 

 reiiulTat.ion dos Spermatozdidcs dans I'CEuf do la Grcnoiiillc," ' Bull. dcrAoad. 

 roy.de I'clf^ifiiic,' 3mc, ser., t. xviii, No. 8, 18S9. 



* Buller, " Cohlriijulions (o our Knovvlcdf,'0 of Uic I'liysioloffV oi I lie Spcr- 

 nialozoa orFern.s," ' Aiui. oi Botany,' vol. xiv, I'JOO, p. 543. 



