24 



PROTOZOA. 



the 10 1 0u th part of an inch in diameter. If one of them be selected for 

 observation, it will be found to be composed of its proper cell-wall, a 

 number of granules fixed to its upper and inner surface, and towards 

 its centre generally one or more hyaline vesicles. 



Fig. 11. 



1. Kemarkable forms assumed by Proteans developed from the matter of the seed-like bodies of 

 Spongilla, magnified. 2. General form of large spiculum. 3. Spiniferous spiculum. (After Mr. H. 

 J. Carter). 



(54.) The granules are round or ovoid, translucent, and of an emerald- 

 or yellowish-green colour, varying in diameter below the la> 1 oou th 

 part of an inch, which is the average linear measurement of the largest. 

 In some cells they are so minute and colourless as to appear only under 

 the form of a nebular mass, while in others they are of the largest kind, 

 and few in number. 



(55.) The hyaline vesicles, on the other hand, are transparent, colour- 

 less, and globular, and, although variable in point of size like the green 

 granules, are seldom recognized before they much exceed the latter in 

 diameter. They generally possess the remarkable property of slowly 

 dilating and suddenly contracting themselves, and present, in their 

 interior, molecules of extreme minuteness in rapid commotion. 



(56.) The sponge-cell when in situ is constantly changing its form, 

 both partially and wholly ; its granules also are ever varying their posi- 

 tion, in unison with, or independently of, the movements of the cell ; and 

 its pellucid vesicle or vesicles may be seen dilating or contracting them- 

 selves, or remaining passively distended, exhibiting in their interior the 

 molecules above mentioned in rapid commotion. When first separated 

 from the common mass, an isolated cell for a short time assumes a glo- 

 bular form, and afterwards, in addition to its becoming polymorphic, 

 evinces a power of locomotion ; it emits expansions of its cell-wall in 

 the form of obtuse or globular projections or digital and tentacular 

 prolongations. 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 globular mass. Should a spiculum chance to be placed 

 in the path of a cell thus in motion, it will ascend it and traverse it 



