404 ON INSECT ANATOMY. 



preserve them in unchanged position under the action of the knife. 

 The following plan which has been found most successful in making 

 sections of diseased structures, and is employed by Professor E-anvier 

 appears to me the most suitable for the purpose. 



Place the parts (or the whole insect taking care to make such 

 punctures or slits in the integuments as will allow the fluids used 

 to penetrate thoroughly,) in alcohol for 24 hours, a time sufficient to 

 to fix, without contracting the tissues. Then, in solution of picric 

 acid for a few days, by which the spirit is expelled and the parts 

 are again slightly hardened. After a few days wash in pure water 

 and plunge the preparation into a weak solution of gum arable which 

 completely penetrates the tissues in a few days. Then remove and 

 place in alcohol, which takes up the water, and the gum solidifies 

 and yields a mass which resists uniformly the cutting blade — micro- 

 tome, or razor — according to convenience. "When the section is made, 

 the gum dissolves out after soaking a little while in water, and the 

 preparation can be floated in the fluid selected for preserving it. 

 Cells are of course needed for preparations of larger parts and organs. 



In the cricket's head, to which our attention is now directed, the 

 same sections which were shown in preparations and drawings, 

 displaying the dermo- skeleton, are equally serviceable in indicating 

 the position of the soft parts. It will be seen from the drawings 

 that this cranial dermo-skeleton contains within it a large number 

 of organs which are facial rather than cerebral. The longitudinal 

 vertical section in median line, shows the oral cavity, roofed by a 

 long line of palate with the large and fleshy tongue beneath. At 

 the isthmus of the jaws, suspended by muscles from the vertex of 

 the cranium, the oral cavity becomes continuous with the 

 oesophagus, situate high up, and resting on the central saddle 

 formed by the union of four internal osseous processes, two of 

 which descend from the vertex (one on each side,) whilst the 

 remaining two rise from the base of the skull. Prom this central 

 position the oesophagus, with its bunch of salivary glands, passes 

 down between the two lower processes, into the neck. Nearly the 

 whole of the intra-cranial cavity is occupied by the muscles which 



