THE ANIMAL CELL. 



(figs. 2. and 3) : it would however lead us too far to enter into a 

 description of tlieni here. 



Fig. 2. 



Fiff. 3. 





^{^m i III iiii I i II liiiiiiiiiii ^i|''-^.?i M ' II 11 u/^^-^ •-"<? 



Fig. 2. — Textures seen in a Longitudinal Section of the Leaf-Stalk of a 

 Flowering Plant. 



1, 2, Polyhedral cells (from mutual pressure). 3, 4, 5, Elongated tubular Tviid 

 prismatic cells. 6, Pitted tissue. 7, Spiral vessels. 



Fiff. 3. — Stellate Vegetable Cells. 



Fig. 4. 



THE ANIMAL CELL. 



Turniug now our attention to the animal embryo, we find that it 

 also is entirely made up of cells (fig. 4), rather smaller it is true 

 than those composing the embryo plant, but, 

 like them, consisting of a granular protoplasmic 

 substance (b) enclosing a nucleus (c) ; this in 

 its turn containing one or more nucleoli. 



And here, at the outset, we encounter a 

 fundamental difference between the cells com- 

 posing the animal aud those composing the 

 vegetable embryo. In the former there is no 

 membranous investment or cell-wall. In con- 

 sequence of this absence of a restraining en- 

 velope the streaming movements of the proto- 

 plasm, which are observable in every cell, whether 

 animal or vegetable, at an early stage of its 

 existence, and in some remain persistent through- 

 out life, are capable, as will hereafter be more 

 fully explained, of efl'ecting chauges both in the 

 form and also in the position of the animal cell.'- 



Before proceeding to inquire into the changes which may occur in 



* The existence of animal cells destitute of envelope, although more insisted on of late 

 ycai-s, has been all along recognised in the study of cell-development, and was exiiressly 

 pointed out by Schwann himself (iMicroscopische Uutcrsuchungen, &c., i?. 209). It has 

 appeared to some that another name should lie used to designate liodies which thus exist 

 in a naked non-vesicular form. Briicke proposed to call them " elementary organisms,'' 

 a term too cumbrous for use. As the first "shaped " products of organisation which appear 

 in the development of all but the lowest organised beings, they might be named " proto- 

 plasts," or, as that name has been already used in a widely diftevent sense — " mono- 

 plasts," but after all, seeing the universal currency of the term "cell," it is probably 

 most convenient and liest to adhere to it, with the understanding that in many cases it is 

 used in a conventional sense. 



Fig. 4. — Three Cells 



FROM EARLY EmBRYO 



of the Cat. Highly 

 magnified. 



h, protoplasm ; c, nu- 

 cleus with nucleolus. The 

 lowermost cell has two 

 nuclei. 



