564 E. A. MINOHIN. 



tion is to be sought in " functional excitation," under the 

 influence of which " the individuals adapt themselves regu- 

 larly, without interruption, and in all their organs" (p. 828). 



Space would not permit of a thorough discussion of all the 

 questions raised by these propositions, but it is a legitimate 

 task to discuss here how far the ontogeny and phylogeny of 

 the spicules support or refute Delage^s views, and to test them 

 by the facts of spicule development. At the outset some con- 

 sequences may be pointed out which follow from his theories. 

 If the adaptation be always ontogenetic, and due to a reaction 

 on the part of the individual organism to a functional excita- 

 tion, then an adaptive structure might be expected to arise 

 only when the conditions to which it is an adaptation have come 

 into operation. If, on the other hand, the adaptation is phylo- 

 genetic, acquired in the past history of the evolution of the 

 species, and fixed and handed on by heredity, there would be 

 nothing astonishing in finding that an adaptation shows itself 

 before it is functional or useful. A prophetic adaptation of 

 this kind would, however, be fatal, it seems to me, to the view 

 that adaptation is always ontogenetic. 



To return now to our spicules. We believe that in phylo- 

 geny they arose by the union of three separate monaxons, 

 which first came to lie one between each pair of pores, and 

 then fused together in trios. A consideration of the structure 

 of the wall shows at once how, when union took place, they 

 met at quite regular angles of 120°. So far all is simple and 

 natural, and there is nothing to contradict the view that in 

 phylogeny the regular forms of the triradiate spicules were pro- 

 duced by " auto-regulation " in response to functional excita- 

 tion. The matter is, however, quite otherwise when we come 

 to the ontogeny. Whatever may have been the past history, the 

 three spicule rays are not laid down at the present day first as 

 three full-sized monaxon spicules, and then secondarily united 

 into one system. The supposition that they ever were formed 

 in this way is purely theoretical. They are, on the contrary, 

 united to form a triradiate system when still excessively 

 minute and enclosed within their secreting cells. This 



