146 



GEODIA AGASSIZII. 



generally speaking, different, and we may therefore expect to find certain dif- 

 ferences in the spicules. The question therefore arises whether all the differences 

 observed are entirely due to the differences of the external forces which acted 

 on the growing sponges, or whether they are in part germinal (hereditary) 

 in character. 



None of the differences in the shape and relative frequency of the spicules 

 seems to me to exceed the limits allowable for such somatic (individual) non- 

 germinal (non-hereditary) variation. The average and maximum deviations 

 of the dimensions of the oxyasters, sterrasters, large amphioxes, and ortho- 

 pi agiotriaenes from the mean are only 4.46-13.91 and 6.1-28.6 % respectively, 

 and also fairly within these limits. The average and maximum deviations of the 

 dimensions of the small dermal amphioxes, anatriaenes, and mesoprotriaenes, 

 which range from 9.41 to 29.93 and from 20.1 to 91 % respectively, are so con- 

 siderable that at first sight it seems necessary to consider them as germinal. 

 The greatest deviations are observed in the length of the clades of the anatriaenes 

 and the clades and epirhabds of the mesoprotriaenes, the total range of maxi- 

 mum deviation of the latter exceeding 130 %. 



The position of the oxyasters, sterrasters, orthoplagiotriaenes, and large 

 amphioxes is different from that of the small amphioxes, anatriaenes, and pro- 

 triaenes. The former lie within the sponge and are thus to a certain extent 

 sheltered from the influence of the external forces; the latter lie superficially 

 and are protruded more or less beyond the sponge and thus more exposed to the 

 external forces. These external forces are different in the nine stations. It is 

 therefore only to be expected, that the last named, exposed, spicules on which 

 the external forces act more directly, should be much less constant than the 

 first named, sheltered ones, on which they act more indirectly. 



These facts and considerations clearly show that the peculiarities of the 

 internal spicules must be systematically much more important than the pecu- 

 liarities of the protruding ones. I therefore thought it desirable to ascertain 

 what systematic result an examination of the internal spicules by themselves — 

 leaving the external ones out of account — would lead to. To do this I selected 

 the most accurately determinable dimensions of the internal spicules, namely 

 the length of the sterrasters and orthoplagiotriaene-clades and the length and 

 thickness of the large choanosomal amphioxes and orthotriaene-rhabdomes. 

 These six dimensions of each lot I compared with the six corresponding dimen- 

 sions of each of the other eight lots. In each of the thirty-six possible pairs 

 (combinations of nine in the second class without repetition) I added up the 



