258 



JOHN W. SCOTT. 



alone or to differences in reproduction, should they prove gener- 

 ally true for other annelids. 



Another series of experiments showed the extreme lightness of 

 the sperm; their specific gravity in sea-water being between 

 1.038 and 1.046. In contrast to eggs which increase in density 

 as they mature, the sperm masses decrease in density as they 

 grow larger and finally break up into free-swimming sperm. So 

 that the density of the ripest sperm is even less than 1.038, as 

 shown in Table IV. This density is interesting when considered 



TABLE IV. 

 To SHOW THE SPECIFIC GRAVITY OF SPERM. 



Test 

 No. 



Density of 



Solution 



Used. 



Material Used. 



Result of Cemrifuging. 



8 



40 

 42 

 43 

 44 

 45 

 48 

 50 



52 

 55 

 56 



1-075 



1-075 

 1.070 

 1.062 

 1.051 

 1.038 

 1.046 

 1.041 



1.046 



1.051 



1.038 



Contents of ccelome. 



Sperm shed in sea-water. 

 Sperm shed in sea-water. 

 Sperm shed in sea-water. 

 Sperm shed in sea-water. 

 Sperm shed in sea-water. 

 Sperm shed in sea-water. 

 Ccelomic contents of worm 



that deposited sperm on 



previous day. 

 Coelomic contents of worm 



that deposited sperm on 



previous day. 

 Coelomic contents of worm 



that deposited sperm on 



previous day. 

 Coelomic contents of worm 



that deposited sperm on 



previous day. 



All sperm on top. All cor- 

 puscles sink. 



All sperm on top. 



All sperm on top. 



All sperm on top. 



All sperm on top. 



All sperm at bottom. 



All sperm on top. 



All unripe sperm sink; a few 

 nearly ripe on top. 



Younger sperm masses sink. 

 Older sperm masses on top. 



Younger sperm masses sink. 



A few lightest, ripest sperm 

 on top. 



in connection with fertilization and the habitat in which the 

 animal lives. Water currents are undoubtedly important factors 

 in the dissemination of sperm. But the sand flats on which 

 these animals are found are securely protected from violent cur- 

 rents, where reefs or eel grass or shoals of adjacent islands break 

 the force of the changing tide. The limited range of the animal 

 does not require a wide scattering of the sperm. In fact the 

 density of the sperm is such that, in the presence of very gentle 

 currents, their distribution must be very limited at the time of 

 oviposition. But the lightness of the sperm provides an easy 



