170 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



after the pieces had been in contact for less than a day. In 

 the fourth pair, however, the edge of one piece was con- 

 siderably thicker than that of the other, and contained 

 more ampullae; so that after the edges met, the thicker edge 

 was pushed over the thinner one instead of against it. 

 During the next day, however, the number of ampullae in 

 both edges increased, and a rearrangement took place, 

 when both edges were found squarely pressed against each 

 other. On the day following, fusion had been accom- 

 plished. This case brings out more strongly the fact that 

 there is a certain amount of resistatice that is overcotne by 

 the mutual pressure of the edges before the fusion can take 

 place. 



It might be supposed that this pressure was needed to 

 bring the ampullse into such close contact that their pulsa- 

 tions^ would not interfere with their union. But this does 

 not appear to be the case; for in spite of much searching, 

 it was impossible to find two fused ampullse. The reason 

 for this absence of fusion may perhaps be found in the 

 pulsations of these organs; but it is probable that it must 

 be sought in the mutual repulsion of the ampullae; for, even 

 in the same colony they do not fuse, so far as is known, 

 and in adjacent colonies they are often seen so closely 

 appressed that no intervening substance can be detected, 

 and their pulsations do not materially decrease the area in 

 contact; but still no fusion occurs. 



The first change that is observed in two colonies that are 

 about to fuse is that some of the ampullae from one or both 

 colonies penetrate the test of the other. These grow past 



1 Pizon (1900, p. 64) in discussing the results in the writer's paper on the contractile 

 function of the vascular ampuUffi (Bancroft, 1899) conies to the conclusion that other 

 more convincing facts must be brought forward before it can be admitted that the walls 

 of the ampullae have the power of contractility. In the main, this would be true for the 

 facts which Pizon discusses; for, although offering strong evidence for the independent 

 contractility of the ampullae, they do not prove it beyond doubt. But the writer cannot 

 agree with the illustrious French ascidiologist that the power of contraction of the am- 

 pullae is left at all in doubt if the full evidence offered in the paper mentioned is taken 

 into consideration. He does not give more than a passing mention to the principal fact 

 upon which this power was based, and apparently does not consider it in arriving at 

 his conclusion,— the fact that the pulsations of the ampullae continue after all the buds 

 and zooids of the colony have been removed. To the writer this is absolutely convincing, 

 and it seems that no stronger evidence could be adduced. 



