DEVELOPMENT OF CUCUMARIA ECHINATA 299 
divergences, one-third, one-quarter, two-sevenths, three-elevenths, 
&e., show a gradual approximation to the angle of about 99° 30’. 
The angles seem to undergo no variation from different degrees 
of contraction, for only longitudinal muscle fibres are present 
in the wall of the tentacle. 
* Hand in hand with the regular spiral arrangement of branches, 
TExtT-Fic. 10. 
A. Tentacle of young, viewed from external side to show the manner 
of branching. B. One of the ventral pair. x40. P,_,,= 
branches of the first order; S,_,,=same of the second order ; 
T,_, = same of the third order. 
supporting calcareous bodies lie in spiral distribution, always 
on the side where a branch is given out.’ 
In the young, whose length exclusive of tentacles measures 
2-5-4-5 mm., the regular manner of branching as referred to 
above is plainly visible. In the eight tentacles, other than the 
ventral pair (Text-fig. 10, a), there are about a dozen branches 
R2 
