NATURE STUDY IN SCHOOLS. 



225 



tion of the termination of the twig, we can ascertain whether a sponge is 

 growing in any particular direction or not. 



Of coursa as the skeleton is formed from the sarcode, or sponge flesh, 

 fiis always grows in advance of the horny fiber. The fleshy matter is rath- 

 er more dense around new fiber, especially around the tips of the growing- 

 twigs. When division of the twig is about to take place, the thicker saicode 

 becomes more bulbose about the extreme tip of the growing twig than at 

 other times, and in this bulb the division of the twig occurs. See 109, (', 

 a, where there is a divided twig, and compare with b, in which division 

 is not taking place. 



B a 



in % \\ 



c 



Fig. 109. 



cc 



n W K 



o a 



D 



E 



Fiber of Orange Tube Sponge. A and B arrested twigs from the inner tube. C, new growths. 

 D E and F, new anastomosing against old; a, old growth; o, new. 



I may here say, in passing, that the best way to examine the skeleton 

 for a new growth is in an alcoholic specimen. The flesh may be easily re- 

 moved, bit by bit with a needle, taking care not to break the delicate ter- 

 minal fibers. But although it is quite easy to satisfy one's self as to the 

 methed of growth, it is not always easy to find a twig in the act of divi- 

 ding. I have, however, found several, and have a number of times traced a 

 complete series, from the very earliest division to the point of anastomosis 

 or to arrested growths. 



The growth at the terminal portion of the tube is most rapid, and < f 

 course upward and slightly outward, but never inward, and branches of the 

 fiber ci.itinue to grow, sending out many twigs before any anastomosis taki 

 place. Or in other words, that portion of the cylinder which is the most ad- 

 vaiceA, proinces branching fibers which push upwards without anastomosis : 

 fibers which send out lateral branches are the ones which anastomose. An- 



