92 Mr. H.J. Carter on the Freshwater Sponges of Bombay. 
partially and wholly ; its granules also are ever varying their po- 
sition with, or independently of, the movements of the cell, and 
its pellucid vesicle or vesicles dilating and contracting themselves 
or remaining passively distended, and exhibiting in their interior 
molecules of extreme minuteness in rapid commotion. When 
first separated from the common mass, this cell for a short time 
assumes a globular form, and afterwards, in addition to be- 
coming polymorphic, evinces a power of locomotion. During its 
polymorphism it emits expansions of its cell-wall in the form of 
obtuse or globular projections, or digital and tentacular prolon- 
gations. If in progression it meets with another cell, both com- 
bine ; and if more are in the immediate neighbourhood, they all 
unite together into one common globular mass. Should a spicu- 
lum chance to be in the course of a cell, it will ascend it and tra- 
verse it from end to end, and, subsequently quitting it or assuming 
its globular form, embrace some part of it and remain stationarily 
attached to it. The changes in shape and position of the sponge- 
cell and its intercellular mucilage are for the most part effected 
so imperceptibly, that they may be likened to those which take 
place in a cloud. Its granules however are more active ; but there 
appears to be no motion in any part of the cell, excepting among 
the molecules within the hyaline vesicle, which im any way ap- 
proaches to that characteristic of the presence of cilia. 
It should be understood however that these remarks are not 
applicable to every sponge-cell, although fully developed, which 
appears in the field of the microscope, but rather a statement of 
what a sponge-cell may evince, than one of what every sponge- 
cell does evince. 
The polymorphic cells or proteans which appear in the watch- 
glass after the contents of a seed-like body have been forcibly 
expelled into it under distilled water, are much more active in 
their movements. Their cell-walls frequently assume the most 
fantastic figures, spheroidal, polygonal, asteroid, dendritic, &e. 
Their green granules move backwards or forwards, to this side 
or to that, with great activity, as the part of the cell to which they 
are attached is attracted in one direction or another ; while their 
hyaline vesicle or vesicles (in progression) appear occasionally in 
every part, not only of the body of the cell, but in its tubular 
prolongations. The contraction of the hyaline vesicle seems to 
take place most frequently when it arrives at the posterior extre- 
mity, that is, according to the direction in which the cell is pro- 
gressing ; next in frequency at the sides, seldom in the anterior 
or central part of the mass. When contraction takes place it is 
effected more or less completely, more or less suddenly ; if com- 
plete, a dark speck or opacity marks the original position of the 
vesicle, in the centre of which, if watched, it may be observed to 
