FKIITILISATION OF THE EGGS OF ANIMALS. 151 



cheniotactic substance which is excreted by the living eg-g 

 and diffuses through the gehatinous coat into the surrounding 

 water ? 



2. After a spermatozoon has come in contact with the outer 

 surface of the gelatinous coat^ is it retained there mechani- 

 cally^ or in consequence of a tactile stimulus exerted upon it 

 by the surface ? 



3. Does the spermatozoon bore through the gelatinous coat 

 radially ? If so, wliy ? 



4. After reaching the outer surface of the living egg (i.e. 

 the protoplasm), what is the nature of the forces which lead 

 the spermatozoon to unite with it ? 



5. Closely connected with the latter is the further question : 

 by what means is the progress of a spermatozoon from the 

 surface to the interior of an egg brought about ? 



III. Material. 



The following species of Echinodermata were made use of : 



f Echinus microtuborculatus, Blv. 

 Class Echinoidea | Sphterechinus granularis, Ag. 

 Regulares jArbacia pustulosa, Gray. 



i^Strongylocentrotus lividus, Brdt. 

 Irregulares Echinocardinm cord at us, Gray. 

 Asterias glacialis, O.F.M. 



Class Asteroidea • ^ tt. i • , •, t\t-ii t 



thclunaster sepositus, Mull. I r. 



[Cjphioderma longicauda, Miill. Tr. 



Class Ophiuroidoa i r^ i • i i i t- t 



^ [Ophiogiyplia lacertosa, Lyman. 



Class Ilolothnroidea Ilolothuria Stellate, D.Ch. 



Class Crinoidea . Antedon rosacea, Norman. 



Observations upon the motility, especially in regard to 

 surfaces, were made upon the spei'matozoa of all the above 

 species. The experiments and observations upon fertilisa- 

 tion were restricted to the first three Echinoidea, namely. 

 Echinus, Sphaerechinus, and Arbacia. 



