264 GENERAL ANATOMY OR HISTOLOGY OF BLOW FLY. 



termed the matrix. This matrix may be laminated, and the 

 cuticle of insects has been regarded by some as substantially 

 an intercellular matrix. Other matrices exhibit a distinct 

 fibrillation, as in fibro-cartilage, but I am in doubt if such are 

 ever found in insects, although fibrillation of the cuticular layer 

 has been described in Crustacea and Arachnids. 



The various tissues may be arranged according to their 

 origin. Thus the epithelial, nervous and muscular tissues are 

 developed from the cells of the blastoderm, whilst the amoe- 

 boid cells and the connective tissues originate from the 

 parablast. 



The principal modifications exhibited by cells and nuclei 

 may be conveniently considered first, and a description of the 

 several tissues classified under the subjoined heads will follow : 



1. The parablastic tissues. 



2. The epithelia ; and 



3. The muscles and nerves. 



1. CELLS AND NUCLEI. 



Cells. The parts called cells are corpuscles, which are very 

 similar in insects and in all other animals ; indeed, they cannot 

 be said to differ in any essential character from those of which 

 the human body is built. In the fly the largest cells are T v 

 of an inch in diameter, or twice as large as the largest in the 

 human body, whilst the smallest do not exceed TT nhnr of an inch, 

 and are smaller than any of those found in the tissues of man. 

 Some cells have a distinct outer wall, or cell-wall ; all possess 

 a main substance termed cell-substance, or protoplasm ; and 

 all have a central body imbedded in the protoplasm, termed the 

 nucleus. 



The Cell Substance, or protoplasm of a cell, consists of a fine 

 reticulum, or network, radiating from the nucleus, termed 

 spongioplasm, and of an apparently structureless substance, 

 which occupies the meshes of the spongioplasm, known as 

 liyaloplasm or cncliylcma. 



