18 



ANIMALS AND PLANTS. 



the cell itself; the vegetable cell being surrounded outside its pri- 

 mordial utricle by a thick non-nitrogenous cuticle, the cellulose 

 capsule ; while the animal cell possesses a very delicate nitrogenous 

 membrane, or instead of this only a more viscous boundary layer of 

 of its own semi-fluid contents. Nevertheless, there are also vegetable 

 cells provided only with a simple naked primordial utricle ; and, on 

 the other hand, animal tissues which resemble vegetable tissues in 

 the fact that the cells remain independent and develop a capsule 

 (Chorda dorsalis, cartilage, supporting cells in the tentacles of hydroids, 

 fig. 6). 



FIG. 6. a, Vegetable parenchyma (after Sachs). I, Axial-cells from the tentacles of Cam- 



panularia. 



Neither can we, as has been done by many investigators, regard the 

 multicellular composition of the body as a necessary sign of animal 

 life. For not only are there many iinicellular algae and fungi, but 

 also animal organisms which are composed of one simple or complexly 

 differentiated cell (Protozoa). Finally, it is not possible to see any 

 reason why unicellular animals should not exist, especially when we 

 consider that the cell forms the starting-point for the development of 

 the animal body. 



3. Least of all can a test be found in the reproductive processes. 

 In plants indeed we find a predominance of the asexual method of 

 increase by spores and buds, but similar methods of increase are 

 widely present amongst the lower and more simply organised ani- 

 mals. Sexual reproduction is effected both in animals and plants by 

 processes which are essentially similar ; consisting in both of the 

 fusion of the male element (spermatozoon] with the female element 

 (ovum] ; and the form of these elements presents in both kingdoms a 

 great agreement, at any rate they are in every case derived from 

 cells. The structure and position of the generative organs inside the 

 body, or as outer appendages of it, cannot be regarded as a distin- 

 guishing mark, inasmuch as in both kingdoms the greatest difference 

 prevails in this respect. 



