OKGANIZATION OF RENILLA 501 



Both these states, however, were quite obviously dependent upon 

 internal pressure relations and yielded no evidence in favor of 

 the view that one autozooid has effective nervous connections 

 with another, and thus acts in unison with its neighbor. In 

 fact, the evidence seemed conclusive that so far as nervous or- 

 ganization is concerned the autozooids are strikingly independ- 

 ent of one another and resemble in this independence the separate 

 fingers of such a sponge as Stylotella. 



The control of the pressure relations within the body of Renilla 

 is accomplished by a mechanism that has been more or less 

 worked out by previous investigators. If a freshly collected 

 Renilla is placed in a basin of sea-water, its volume will be found 

 to be much reduced and its autozooids mostly contracted. 

 Gradually it will be observed to become more and more inflated 

 and its autozooids will slowly expand, as already described by 

 Miiller ('64, p. 354). During the time the Renilla is filling it- 

 self with water, for such the operation is, the peduncle exhibits 

 rhythmic contractions that have a striking resemblance to in- 

 testinal peristalsis. At each onset of activity a wave of con- 

 traction can be seen to start in the region where the peduncle is 

 attached to the rachis and proceed thence to the distal end of 

 the peduncle. Waves of this kind run over the peduncle with 

 considerable regularity and occur ordinarily every thirty-five to 

 forty-five seconds. The regular association of this movement of 

 the peduncle with the distention of the body of Renilla suggests 

 that the activity of the peduncle is the chief means of accom- 

 plishing the distention of the colony as a whole and the canal 

 ■system within the colony supports this idea. 



If a Renilla is anesthetized with magnesium sulphate and the 

 peduncle is cut transversely, this body can be seen to consist of a 

 stiff-walled tube containing, as has long been known (Miiller, 

 '64; Verrill, '66-'69; Kolliker, '72; Eisen, '76), two canals, one 

 (the inferior) about twice the cross-section of the other. These 

 canals are separated by a thin firm membrane, the transverse 

 septum. If the larger cavity is injected with sea-water contain- 

 ing some indifferent coloring matter in solution, such as methy- 

 lene blue, the colored fluid passes freely into the cavities of the 



