42 LABORATORY STUDIES IN ZOOLOGY 



cells. Identify the delicate membrane or sarcolernma which 

 covers each fiber. This thin covering is best seen in places 

 where the fibers are crushed or broken apart. Each fiber shows 

 both a longitudinal and a cross striation. The longitudinal 

 st rial ion is due to minute strands, the fihrillce, which extend the 

 length of the fiber and are bound together in the same sarcolemma 

 sheath. The transverse striations are due to alternately dark 

 and light bands in the fibrils. Each muscle cell also contains a 

 number of spindle-shaped nuclei scattered among the fibrils. 

 The young muscle cell possesses but a single nucleus which during 

 growth divides repeatedly, resulting in the multinucleate 

 condition. 



Make a drawing which will show all the structures listed 

 above. 



Non-striated Muscle. — Study a stained preparation. Non- 

 striated muscle tissue is composed of long, slender, spindle-shaped 

 cells arranged parallel to each other. Each long fiber or cell 

 possesses an oval nucleus near its center. 



Make a drawing of a single fiber, showing parts described. 



Nervous Tissue. — A nerve cell, or neuron, consists of a central 

 portion, called the cell body, which contains a large nucleus, and 

 of slender processes which extend out from this cell body often 

 to great distances. Portions of nervous tissue which consist 

 predominantly of cell bodies are spoken of as gray matter, while 

 those which consist of the processes constitute the white matter. 

 The processes of a nerve cell are of two kinds: those which convey 

 the impulses toward the cell body, called dendrites, usually very 

 numerous and much branched, and those which convey the 

 impulse away from the cell body, usually single and unbranched 

 or slightly branched, called the neurite or axone. What one 

 refers to as nerves are bundles of these processes. Histologically, 

 nervous tissue consists of (1) the nervous matter proper, i.e., nerve 

 fibers or neurones, and (2) delicate supporting and connective 

 cells called neuroglia cells, in which the nerve cells are embedded. 



Study a cross-section of the spinal cord of the frog. Under 

 low power identify the narrow dorsal fissure and the broader 

 ventral fissure. Notice that the cord differs in appearance in 

 different parts. There are two general regions, a central, slightly 

 darker region, the gray matter, trapezoidal in shape and contain- 

 ing numerous darkly stained cell bodies; and an outer, lighter 

 region, the white matter, with only a few small cell bodies. The 



