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 in 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, &c. 

 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 



