1895.] Sponges: Recent and Fossil. 539 
converted into sexual products. Itis even supposed from the 
connection of certain cells by ganglia with groups of other 
cells, that there may be a few nerve fibres, with the power of 
converting external i impressions into muscular movements. 
The life history of sponges is, as yet, imperfectly known. 
Our knowledge can be given in a comparatively few words. 
Increase takes place by internal and external budding; by fis- 
sion (division); and by sexual reproduction. In the method 
of increase by budding, a few cells become developed at some 
point, increase by general growth, bulge out from the cortex, 
and drop off to form a new colony. In internal division a 
mass of cells forms a globular cluster. The outer ones change 
so as to form an external sac. Under certain conditions the 
cells from the interior creep out from the enclosing sac, form 
a spreading mass, and give rise to a new colony. Sollas sup- 
poses these “gemmules” serve a PPAP IUNE purpose, and in- 
sure the persistence of the race, “since,” says he, “they only 
appear in extreme climates on the approach of drought, and 
in cold ones on the approach of winter. As a secondary 
function they serve for the dispersal of the species; some are 
light enough to float down a stream, but not too far, so that 
there is no danger of their being carried to sea; others which 
are characterized by AT air chambers, are possibly distrib- 
uted by the wind.” 
- Both sexes may occur in the same colony—though frequently 
one predominates—or they may be entirely separated. The 
ovum or female form develops from one of the wandering 
cells previously referred to, gradually increasing in size and 
finally passing into a resting state. The spermatozoan or 
male element is a minute oval or pear-shaped body with a 
long vibratile tail. The tailed bodies are also developed from 
wandering ameeboid cells, each cell containing numbers of 
` them. When mature, the spermatozoa rupture the walls of 
the sac where they are confined, and at a favorable opportun- 
ity enter and fertilize the ovum. After this occurs the egg be- 
gins to grow, the cells at either end assuming distinct char- 
acters. When mature, the new individual ruptures the cell 
wall, enters one of the canals ramifying throughout the sponge 
