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 with 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. 



Dimension 



Maximum deviation 



Total range of 

 maximum 

 deviation 



Averages of the 

 deviations of the 

 9 lots 



above tlie mean 



below the mean 



per cents of tlie respective dimensions 



Breadth of sterraster 



6.1 



7.4 



13 . 5 



4.46 



Length of orthoplagiotriaene-elade 



10 



12.8 



22.8 



4.64 



Length of sterraster 



1.3.9 



9.2 



23.1 



6.61 



Length of large amphiox 



17.9 



17.9 



35.8 



8.83 



Thickness of large amphiox 



28.6 



14.3 



42.9 



10.60 



Thickness of anatriaene-rhabdome 



22.8 



20.1 



42.9 



9.41 



Thickness of orthoplagiotriaene- 

 ruabdome 



23.9 



20.3 



44.2 



13.91 



Length of orthoplagiotriaene-rhabd- 

 ome 



18 



26.3 



44.3 



12.17 



Diameter of oxyaster 



28 



17.4 



45.4 



10.20 



Thickness of small dermal amphiox 



32.5 



22.7 



55.2 



14.18 



Thickness of mesoprotriaene rhabd- 

 ome 



35.4 



24.3 



59.7 



17.21 



Length of small dermal amphiox 



40.4 



21 



61.4 



13.19 



liCngth of anatriaene clade 



22 7 



43.3 



66 



15.49 



Length of mesopi-otriaene clade 



54.5 



41.3 



95.8 



22.51 



Length of mesoprotriaene epirhabd 



91 



43 



131 



29.93 



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, 



