228 



SYSTEMATIC ZOOLOGY roll TEACHEBS. 



ing passed a little beyond the sarcodc into the lining membrane of the tube. 

 Or rather this is the condition under which such twigs are found, but it is 

 quite probable that the lining membrane has absorbed a portion of the sar- 

 code and grown around the twigs before the usual quantity of horny mat- 

 ter was deposited on their extremities' . 



Variations in Skeleton Growth. 



I have said that new fibers usually anastomose with new growths, and 

 this is true where an unbroken internal membrane occurs ; thus this is the 



Fig. 112. 



r 



A 



B 



Young Tube Sponge, life size. A. who'.e sponge, E, section; a, terminal closing membrane; b' 

 extra cosing membrane in 1 ro .en portion. 



normal method of growth, but where' new and growing fiber comes in con- 

 tact with an old growth, a kind of anastomosis takes place. In this ease 

 the growing tip of the new twig comes in contact with the horny side of the 

 old growth anel is soldered there by an accumulation of additional of horny 

 matter, secreted quite likely by both the old and the new sarcode. But in 

 all such anastomosis there is no connection between the internal hollow mem- 

 brane of the fiber of one growth with that of another. That is, the gicwth 

 does not penetrate into the horny covering of the old growth as it does into 

 the membrane of the new. 



Another peculiar feature of this method of anastomosis is that when the 

 new growth comes in contact with the old, the new twig, no matter at what 

 angle it comes against the horny side of the old growth, usually continues to 

 grow for a short distance, thus ensuring a greater surface of attachment. 

 But as I have never succeeded in finding a case where this growth continued 

 beyond the point ot jointure, it is probable that the horny matter, was se- 

 creteel by the sarcode upon both the old branch and the new twig, thus pre- 

 venting further growth. 



