134 THE MICROSCOPIST. 



to be formed. Lastly, Dr. Carpenter thinks it may disperse 

 itself still more completely into its component granules ; by 

 the reunion of which certain peculiar vibrating filaments (the 

 so-called spermatozoa), may be formed. 



" In the lowest and simplest forms of living beings," says 

 Dr. Carpenter, " such as we meet with among the humblest 

 cellular plants, we find a single cell making up the whole 

 fabric. This cell grows from its germ, absorbs and assimilates 

 nutriment, converts a part of this into the substance of its 

 own cell-wall, secretes another portion into its cavity, and pro- 

 duces from a third the reproductive germs that are to continue 

 the race; and having reached its own term of life, and completed 

 the preparation of these germs, it bursts and sets them free 

 every one of these being capable, in its turn, of going through 

 the same set of operations. In the highest forms of vegetable 

 life, we find but a multiplication of similar cells ; amongst which 

 these operations are distributed, as it were, by a division of labor ; 

 so that, by the concurrent labors of all, a more complete and 

 permanent effect may be produced." 



Of the development of animal tissues, Todd and Bowman 

 present the following interesting account, in their " Physiolo- 

 gical Anatomy and Physiology of Man." 



" The prevailing mode in which the development of animals 

 takes place, is by the formation, within the parent, of a body 

 containing the rudiments of the future being, as well as a store 

 of nutrient material sufficient to nourish the embryo for a 

 longer or shorter period. This body is called the ovum or egg. 

 It is of thatfform which, in a former page (see Fig. 39, page 

 131), has been described and delineated as the simplest which 

 organization produces. It consists of a vesicular body filled 

 by a fluid, and enclosing another, within which is a third, con- 

 sisting of one or more minute, but clear and distinct granules. 

 The first or vitelline membrane of the ovum, is the wall of a 

 cell ; it is composed of homogeneous membrane : the second, 



