DISSECTION OF ANIMAL TISSUES. 361 



reptiles, the smallest in birds. The fibrillas may be well dis- 

 played in the muscle of some of the Crustacea, even the shrimp 

 and the lobster will show them after they have been boiled ; 

 but the best specimens of aU may be obtained from the muscle 

 of the pig, the very exquisite specimens, for the preparation 

 of which INIr. Lealand has become so justly celebrated, are said 

 to be procured from this animal. The voluntary muscular 

 fibres of all the vertebrate animals have transverse strife ; but 

 the involuntary, with the exception of those from the heart, 

 are without them. In the invertebrate series, according to 

 Mr. Busk, the articulate animals, such as insects, have striae ; 

 but the other classes, such as the moUusca and cephalopoda, 

 although higher in the scale, rarely have markings at all. The 

 involuntary fibres are best procured by being dissected from 

 the muscular coat of some part of the intestine or the stomach 

 of animals : they are more diiScult of separation than those of 

 the voluntary class, and much sooner lose their characteristic 

 structure. The fibres of old animals, and even of young ones, 

 from want of use, sometimes undergo a fatty degeneration; 

 this is shown by a nearly total absence of the striae, and by 

 the presence of numbers of oil globules instead; these last 

 may be known (as will be again pointed out) by their ready 

 solution in sulphuric ether. 



Trachea. — These may be beautifully seen in some of the 

 small parasitic insects, when mounted either in fluid or in 

 Canada balsam (provided the latter has not gained entrance 

 into them, as then they will be more or less indistinct). The 

 arrangement of the large branches, and their communication 

 with the external orifices, termed spiracles, may be well 

 displayed in the perfect insect; but for their minute distri- 

 bution upon the coats of the various viscera, as well as for 

 their examination with high powers, the dissection of each 

 part separately wiU be required. For this purpose the insect 

 should be placed in one of the small troughs with water, and 

 securely fixed to a loaded cork, or to a plate of wax by 

 pins ; the body being laid open, next to the large viscera the 

 tracheae will become visible. The stomach or intestinal canal. 



