. The Journal of experimental zoology. ening the inferior one yielded corresponding results exceptthat there was often much loss of injection fluid at the axial these lines of experimentation show that the superior andinferior canals in the body of the rachis are in communicationwith each other, but by openings not so large as those by whichthey communicate in the peduncle. 362 G. H. PARKER Sufficient facts have now been brought together to allow theformation of a reasonable hypothesis as to the course of thewater through the Renilla colony. (In a resting expanded Re-nilla water is e
. The Journal of experimental zoology. ening the inferior one yielded corresponding results exceptthat there was often much loss of injection fluid at the axial these lines of experimentation show that the superior andinferior canals in the body of the rachis are in communicationwith each other, but by openings not so large as those by whichthey communicate in the peduncle. 362 G. H. PARKER Sufficient facts have now been brought together to allow theformation of a reasonable hypothesis as to the course of thewater through the Renilla colony. (In a resting expanded Re-nilla water is entering the animal through the innumerable poresof its lateral siphonozooids (fig. A).) This water enters in conse-quence of the ciliary action of these zooids. It fills the openspaces of the rachis and from time to time escapes to the exteriorby passing either directly through the minute pores of the rachistissue into the superior canal and out of the axial pore or indi-rectly by passing down the inferior canal of the peduncle to its. Fig. A Diagram of a median section of the rachis (R) of Renilla and of thepeduncle (P) showing lateral siphonozooids (L), aiitozooids (A), inferiorcanal (I), superior canal (S), and pore of the median siphonozooids (M). Thedirection of the current of water in a resting individual is shown by thearrows. distal half where it may pass freely over into the superior canaland thence to the axial pore and out. Of these two outwardcourses that through the peduncle is much the freer and probablythe more usual one to be followed. An indication of the relative freedom of these two courses,as well as a check on the correctness of the hypothesis just ad-vanced, may be gathered from the following experiments. If thepeduncle of a fully distended Renilla be tied off tightly in theregion where it emerges from the rachis, the animal will contractits musculature vigorously, but its volume will remain almost ACTIVITIES OF COLONIAL ANIMALS 363 unaltered. Even the for
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1920
