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POPULAR SCIENCE REVIEW. 
peated process of cleavage or fissigemmation the original sponge- 
monad quickly multiplies itself, though still more rapidly and 
effectively by the subsequent encvstment and breaking-up of the 
monad bodies into spores. In the independent collar-bearing 
types, as already shown, the germs or spores resulting from this 
process of encystment are discharged into the surrounding water, 
and thus dispersed to considerable distances. In the sponges, 
however, this act of encystment takes place within the substance 
of the syncytium, and within its substance are the spores released. 
In this element, moreover, they immediately find a most appro- 
priate nidus or matrix for their future development, and are to 
be encountered on examination in every phase of transition. 
As it has been previously shown that the larval or initial con- 
ditions of the independent collar-bearing monads take the form 
of either amoebae or simple flagellate monads, so also it will 
be found that the collar-bearing sponge-monads commence 
existence as similar simple units. Aided, indeed, by the light 
afforded by the developmental phenomena of this independent 
group it is easy to recognize that the amoebiform bodies of every 
variable shape and size dispersed among the syncytial element of 
the sponges are merely the larval or transitional conditions of 
the adult collar-bearing monads which they ultimately resemble. 
Between the amoebiform and the adult state there is usually 
also an intermediate stage, in which the sponge-monad, not 
having yet acquired the characteristic collar, possesses a single 
lash- like flagellum. An illustration of such intermediate flagel- 
late types, taken from an example of a siliceous-spiculed sponge, 
Halichondria panicea , will be found represented at Plate III. 
fig. 32. 
In addition to developing by fission, or as simple units or 
individuals, from the amoeboid to the collar-bearing stage, and 
thus contributing to the further extension of the parent colony, 
it remains to be mentioned that in many, if not all, sponges 
there is another process of development attended with more 
complex phenomena, contributing to the production of de- 
tached and free-swimming monad-aggregations specially adapted 
to secure the wider distribution of the species. In this instance 
the amoebiform units, either as mature cytoblasts or as collar- 
bearing monads returned to an amoeboid state, fuse or coalesce 
intimately with one another in variable numbers, producing 
by such an amalgamation an amoebiform body of considerable 
size. By a process of geometrical cleavage or multiple fission,. 
hundreds of separate individuals all enclosed within a common gelatinous 
investing sheath, and presenting a general aspect clearly resembling that of 
the fresh-water sponge, Spovgilla jluviatilis , with which it is frequently asso- 
ciated. 
