INVERTEBRATE MORPHOLOGY. 



CHAPTEE I. 



PROTOPLASM AND THE CELL. 



In the examination of organisms presenting the series of 

 phenomena which we term life, the invariable presence of a 

 peculiar semi-fluid transparent or hyaline substance becomes 

 quickly apparent. Whether the organism be a plant or an 

 animal, whether it be of the simplest or of the most complex 

 organization, it is still composed of this substance, which is 

 known as protoplasm, and it may be said that so far as our 

 knowledge extends life never exists except in association with 

 this material. Protoplasm is " the physical basis of Life," 

 and it becomes of great importance that its nature should be 

 fully understood, in .order that the results of its activities, 

 Life, may become more intelligible. 



Much has yet to be accomplished, however, before an accu- 

 rate knowledge of the structural and chemical characters of 

 this substance is obtained, and indeed it is incorrect to regard 

 it as a substance, since it is rather the aggregate of a large 

 number of exceedingly complex chemical compounds, none 

 of which are sufficiently known. From the very nature of 

 things it is impossible at present to get a correct idea of these 

 substances and the relations which they bear to one another, 

 since our present analytical methods are not capable of deter- 

 mining and isolating them in living protoplasm and the mere 

 act of subjecting protoplasm to analysis destroys those very 

 relationships which are the cause of the vital manifestations. 



