372 IVILSOX. [\'0L. IX. 



significance as is advocated in this theory. It is probably an 

 adaptive feature acquired within the group of silicious sponges. 

 Now whether the gemmule larva has independently acquired 

 this adaptation, is open to discussion. I am inclined to believe 

 that it exhibits the feature in question, for the same reason 

 that it develops germ layers : both features come to it as 

 inheritances, the latter from a far distant ancestor, the former 

 from a comparatively near one, both features being of actual 

 physiological use to the larva. 



To repeat, the conclusion I reach in regard to the marked 

 resemblance between the egg larva and gemmule larva of 

 silicious sponges is, that it is one not due to independent 

 adaptation to similar circumstances, but to inheritance from a 

 common source. What I believe I have found is, a bud embryo 

 exhibiting ancestral traits. To illustrate by means of an 

 imaginary example : suppose the bud of a simple ascidian, 

 instead of developing directly into a new ascidian, first devel- 

 oped into an ascidian tadpole, with its notochord, ner\-ous 

 system, etc., we should then have, I take it, a parallel case to 

 the gemmule development of sponges. Only, in the imaginary 

 case there could be no doubt of the larval features being inher- 

 itances, while in the case at hand I am free to admit that this 

 view could be disputed. 



The exhibition of ancestral traits in a bud embryo is perhaps 

 a very rare phenomenon. The supposed occurrence of this 

 phenomenon in Loxosoma has been shown to be without 

 foundation, and Deszo's claim that it does occur in the devel- 

 opment of Tethya buds cannot, in view of the insufficient 

 evidence, be admitted. (Moreover, if Desz5's statement that 

 the Tethya bud is derived from a single cell, be a fact, such a 

 cell could properly be regarded as an undeveloped germ cell, 

 and the " budding " of Tethya would then be a process analo- 

 gous to the " sporogonie " discovered by Metschnikoff in 

 Cunina proboscidea (38), or to the paedogenesis of the Cecido- 

 myia larva, and therefore not a case of asexual reproduction.) 

 In fact but a single instance of this phenomenon, as far as I 

 know, has been recorded for the animal kingdom, previously 

 to the appearance of these observations. The case referred to 



