GEODIA AGASSIZII. 



145 



The graph shows that only very few of the maximum averages (maxima) 

 of the same dimensions of spicules from different lots are identical witli each 

 other, and that not a single one coincides with the mean. The extent of their 

 maximum and average deviations from the mean are tabulated below. 



Having thus ascertained the differences in the spicules and stated them in a 

 manner suitable for discussion, the question of their systematic and zoogeographic 

 significance may be taken up. 



There can be no doubt that external forces, acting on the growing sponge, 

 exert an influence on the shape and the dimensions which the spicules attain. 

 We know that at the stations where these sponges were obtained the bottom 

 temperature and the nature of the bottom differ more or less. From this it 

 follows that the forces which acted on the several lots during growth were, 



