451 



from the rest of the colony would be likely to stimulate whatever la- 

 tent tendency they possess in this direction. Accordingly in several 

 Botryllus colonies that were growing vigorously so that they possessed 

 quite a broad edge containing nothing but vessels and ampullae the 

 greater portion of the colony was removed, leaving only a few pieces of 

 the edge without traces of zoöids or buds. When these pieces were 

 examined on the next day a well defined circulation was seen to be 

 established, the blood travelling for a short distance in one direction 

 and then in the other. The source of this circulation was soon located 

 in the ampullae which Avere seen to be contracting rythmically, driving 

 the blood out, and then sucking it up again as they expanded. An 

 examination of uninjured colonies showed that all the ampullae nor- 

 mally carry out pulsations, and that the contractions of neighboring 

 ampullae are very well coordinated so that they are all executed at 

 the same time. But, before I proceed to discuss these phenomena, a 

 Avord about the fate of the isolated pieces. 



They never regenerated a colony, none of the ampullae showed 

 the least tendency towards budding, but the vitality of the pieces was 

 remarkable. On the second day the thickened cylindrical epithelium 

 usually present at the tips of the ampullae had been resorbed. Later 

 the ampullae and the blood cells they contained grew more opaque, 

 and the former became progressively smaller until most of them had 

 entirely disappeared. The piece was then a rich reticulum of small 

 blood vessels with an occasional shrivelled ampulla, the whole filled 

 with blood containing a much greater proportion of cells than normal, 

 but still circulating feebly in alternating directions. The ampullae 

 were still pulsating, but not with enough force to drive the cells out 

 into the vessels. This condition obtained from about the 5*'' day on ; 

 then the circulation became feebler and feebler until it finally stopped. 

 The cessation took place on the 9^^ day in the smallest piece, and in 

 the largest it had not yet occurred on the 15*^ when the experiment 

 had to be discontinued. 



To return to the contractile activity of the ampullae : So far as I 

 know, the only author who has mentioned even the regular flow of 

 blood to and from the periphery of the colony is Pizon ('98, p. 129). 

 He says: 



»Dans une même colonie, les différents cœurs se contractent si- 

 multanément et tous dans le même sens, chassant, par exemple, les 

 corpuscules sanguins et les éléments d'origine régressive dans les am- 

 poules périphériques; puis, à mesure que la pression augmente dans 

 ces ampoules, les battements se ralentissent progressivement et à un 

 certain moment ils paraissent devoir s'arrêter totalement, mais tout à 



34* 



