462 



circulation for two weeks and the greater part of it for a month longer 

 so that this mode of aestivation would be entirely impossible were it 

 not for the ampullar circulation 3. 



Summary. 



1) The ampullae in Botrijllus and Botrylloides normally execute 

 coordinated pulsations. 



2) These pulsations continue after the ampullae are separated 

 from the rest of the colony, but the nature of the coordination 

 changes. 



3) In the various zoöids of the same colony the hearts do not beat 

 synchronously or in the same direction at the same time. As 

 a rule the reversals of the hearts take place at different times. 



4) The rythm of the ampullar pulsations is not affected by the 

 reversals of the hearts of the zoöids. 



5) The pulsations are very slow, the systole averaging 38 seconds 

 and the diastole 33. 



6) The contracting tissue is a thin pavement epithelium composed 

 of polygonal cells in which no fibrous differentiations could be 

 detected. 



7) The coordination of the ampullae is accomplished principally 

 by means of variations in blood pressure. 



8) In the aestivating colony of Botrylloides Gascoi the circulation 

 is kept up almost entirely by means of the ampullae. 



Bibliography. 

 Giard,A., 1S72. Recherches sur les Ascidies composées ou Sj'nascidies. Arch. 



Zool. Expér. T. 1. pp. 501—704. 

 Giard, A., 1891. Sur le bourgeonnement des larves d'Astellium spongiforme Gd. 



et sur la Poecilogonie chez les Ascidies composées. Compt. Rend. Ac. Se. 



Paris, T. 112. pp. 301—304. 

 Herdman, W. A., 1884. On a new Organ of Respiration in Tunicata. Pr. Lit. 



Phil. Soc. Liverpool, V. 39. pp. 39—46. 

 Herdman, W. A. 1886. Report on the Tunicata collected during the Voyage of 



H.M.S. Challenger. Part. II, Ascidiae Compositae. 

 Metschnikow, E. 1869. Entwicklungsgeschichtliche Beiträge. VII. Über die 



Larven und Knospen von Botryllus. Bull. Ac. Sc. St. Pétersbourg, V. 13. 



pp. 293—298. 

 Oka, A. 1892. Über die Knospung der Botrylliden. Zeitschr. f. wiss. Zool. Bd. 54. 



pp. 521 — 547. 

 Pizon, A. 1898. Nouvelles observations biologiques sur la vie coloniale des Tuni- 



ciers fixés (Botrylles et Botrylloides). Compt. Rend. Ac. Sc. Paris, T. 127. 



pp. 127—130. 



Naples, Oct. 22, 1899. 



3 It is probable that in hibernation and aestivation in other genera having a 

 common vascular system the circulation may be maintained by some such means. 



