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resistance though they cannot make headway against a strong pressure. 

 On the other hand it may be maintained that here we have an effect 

 of the conduction of a stimulus by means of the contracting cells 

 along the walls of the vessels. This stimulus is not strong enough to 

 prevent alternate contractions in different regions, but is too powerful 

 to allow adj ace nt ampullae to follow the paths of least resistance, and 

 thus makes them contract together. Both explanations are probable, 

 and I shall not attempt to decide between them, for no matter which 

 one we accept, it must be confessed that the chief explanatory principle 

 for coordination in normal and isolated ampullae is the variation in 

 blood pressure. 



In conclusion I will mention two cases which serve to emphasize 

 the importance of the coordinated ampullar contractions and their 

 power to maintain a circulation independently of the activity of the 

 heart. In narcotizing the Botryllus colony with cocaine the voluntary 

 muscles of the zoöids are first affected, then the heart is stopped, and 

 finally the contractions of the ampullae. Accordingly there is a stage 

 when the hearts have stopped beating but the ampullae still contract, 

 though not always with their full vigor. During this stage it is seen 

 that the ampullar contractions can not only maintain a circulation in 

 the common vascular system, but can also force the blood though some 

 of the zoöids, and through there inactive hearts, though the current is 

 very slow and weak. 



In a colony of Botrylloides Gascoi which I have kept for over 6 

 months in the aquarium at Naples a case of aestivation, or partial 

 lying down in summer, was observed. A more explicit account will 

 he published later, at present we are concerned only Avith the ampullae. 

 While the colony was still apparently in good health a large lobe 

 grew out containing no zoöids, but only ampullae, so far as could be 

 observed in the living colony. Later most of the colony died leaving 

 only this lobe in Avhich a vigorous circulation was maintained by 

 means of the ampullae. These conditions prevailed for about two 

 weeks when the first buds appeared. These were very few in number, 

 and for several generations degenerated without arriving at maturity, 

 often without even opening their siphons. For about a month they 

 did not cover more than about one tenth of the area of the colony, 

 and during part of that time they were so small that they could not be 

 detected with certainty. During this month their hearts cannot have 

 helped much in keeping up the vigorous circulation that was main- 

 tained. Later the buds began to grow faster and gradually recovered 

 their vitality, the part of the colony that contained only ampullae 

 dying. We thus see that the ampullae had to maintain the entire 



