THE ZOOLOGICAL STATION AT NAPLES. 357 



SUt-face be regarded fx'Om the point of view of the spermatozoa, the rotation, 

 with rare individual exceptions, is always in the counter-clockwise 

 direction. 



The rotation phenomenon may be well seen when a drop containing not 

 too many spermatozoa is placed upon an object-glass and examined under 

 the microscope with a magnification of about 300 diameters. If the upper 

 surface of the drop bounded by air be then carefully focussed, the 

 spermatozoa clinging to it appear to the observer to revolve in the clock- 

 wise direction, but when the lower surface bounded by the glass is 

 examined they are seen to move in a counter-clockwise direction. 



The rotation rule was verified for five species of Echinoidea, and for 

 representatives of all the other classes of Echinoderniata. The species 

 examined were the following : — 



ECHINODERMATA, 



Class 1. — HOLOTHUROIDEA. 



Holothuria Stellati, D. Ch. 



Class 2. — EcniNoiDEA. 



Echinus microtuherculatiis, Blv. 



Sphan-echinus granularis, Ag. 



Arbacia pustulosa, Gray. 



Stnmgocenirotus lividus, Brdt. Class S.—Crinoidea. 



1 Antedon rosacea, Norman 



Class 3. — ASTEUOiDEA. 



Asterias glacialis, O. F. M. 

 Echinaster sepositus, Miill. Tr. 



Class 4. — Ophiueoidea. 



Ophioderma lonc/icauda, Miill. Tr. 

 Ophioylypha lacertosa, Lyman. 



It is a somewhat remarkable fact that rotation upon surfaces in a 

 counter-clockwise direction was also observed by Dewitz ' for the sperma- 

 tozoa of certain insects. He believed that the spermatozoa were thus 

 specially adapted for the purpose of finding their way into the micropyles 

 of the eggs. Such an explanation could not, however, apply in the case 

 of the Echinodermata, for no micropyles are present, and the gelatinous 

 zona pellucida is everywhere penetrable. 



The spermatozoa of the Echinoidea easily become attached to glass 

 and other surfaces by the points of their conical heads upon which they 

 often continue to revolve. 



After becoming attached to the zona pellucida the spermatozoa make 

 their way through it in a more or less radial direction. The penetration 

 from the outer to the inner surface of the zona pellucida does not depend 

 upon a chemotactic stimulus, for it was found tliat the phenomenon was 

 equally well seen upon (1) ripe eggs, (2) eggs of full size which had not 

 undergone maturation, and (3) eggs which had been killed with osmic 

 acid and then washed. Penetration of the spermatozoa into the gelatin- 

 ising outer wall of the oosporangium of Cystocyra harhata (one of the 

 Fucacpa>) took place in a striking manner, the jelly becoming densely 

 crowded. The spermatozoa likewise collected in great numbers in the 

 jelly from the cell-walls of seeds of Limnn usatissimum, and also in the 

 zona pellucida of Eihinus eggs after long separation by shaking. 



The entrance of the spermatozoa into gelatinous substances, and also 

 their attachment by the head to living eggs, is connected with their power 

 of clinging and becoming attached to surfaces in general. The more or 



' Dewitz, P/lUgcr's ArcMv, Bd. 38, 1886, p. 358. 



