8 Mr. H. J. Carter on the Anatomy 



Observations. 



Although the above Table includes most of the forms as- 

 sumed by sponges, still it must not be inferred that it contains 

 all ; hence the student can add others to it at discretion. 



Again, the same species, as above stated, may have several 

 forms. Thus the massive form of a species may rise into a 

 bunch of digital processes ; these may again become branched 

 into a tree-like or globular head, after which the branches may 

 unite laterally or by their ends anastomosingly. Or the digital 

 processes may be all on the same plane, simple or branched, 

 &c. ; they might then coalesce partially, so as to present a 

 fenestrated or clathrous form, or, being single and straight, 

 might unite laterally throughout so as to assume a fan-shape. 

 After which the fan-shape has a tendency to assume a con- 

 choidal form (like that of a clam-shell) and finally, becoming- 

 more and more concave, to meet on each side, join up, and thus 

 form a vase, in which there is often a hole at the bottom from 

 the union not being complete. 



In this way a simple may pass into a complicated form, and 

 thus many different forms be produced from evolution (see 

 " Beitrag zur Morphologie und Verbreitung der Spongien," 

 von N. Miklucho-Maclay, Mem. Acad. Imp. des Sci. St. 

 Petersb. 1870, t. xv. no. 3, Taf. 1). 



Composition of Sponges. 



Skeleton generally. 



The general structure of the skeleton is reticular ; and this 

 may be compact or open, tough or tender ; but under this 

 state it may assume any of the forms above mentioned, each 

 of which is not always an indication of a particular species ; 

 for in many instances the same species may assume several 

 different forms, as has just been shown. 



Minute Structure of the Skeleton. 



The element of which the skeleton is composed may be 

 termed " fibre ;" and this is of two sizes, viz. large and small. 

 The large fibre is the oldest, and generally grows vertically 

 or in a direction more or less radiating from the base, in 

 accordance with the general form of the sponge ; while the 

 smaller fibre, which is the younger of the two, unites the 

 large fibres obliquely or transversely. In the skeleton of 

 some species there is such a uniformity of growth that no 



