Uy SPONGES 
as arule over .10 from its termination. In one double sponge, however, I find 
that while in one cylinder it is in its natural condition, in its closely adhering 
neighbor itis at least .40 from the top. (See Fig. 7, where I have given a 
life-sized section of these tubes ; that at B has the membrane in its normal po- 
sition, while that at"A has it much lower.) The width of the membsane va- 
ries greatly ; sometimes there is a mere trace of it, but it is usually moderately 
well developed. The largest membrane which I have ever found in an uninjured 
Young Tube Sponge, life size. A, whole sponge; B, section; a, terminal 
closing membrane : b, extra closing membrane in broken portion. 
sponge, in comparison with its diameter, was in a specimen where it extended 
entirely across the orifice, excepting a narrow opening in the middle, measure- 
ing .05 in diameter. The tube on which this membrane grew was .65 in di- 
ameter, and the membrane was situated about .25 from the termination. ‘The 
next largest membrane was in the tube of the sponge ( given in section in Fig. 
7, B;) a life-sized figure of this membrane is given in Fig, 8, B, and it may 
