1878.] A Lesson in Comparative Histology. . 34I 
the study of the cellular anatomy of even the commonest 
animals, therefore I must resign for the present the wider and 
more attractive field, and descend to details, in order to show by a 
concrete example some of the modifications which cells present, 
and to describe the appearance of some of them when prepared 
for microscopical examination. 
My illustrations are all taken from the common locust, and are 
selected from the results of a recent original investigation on the 
histological structure of that abundant pest. The work was 
undertaken at the desire of Dr. A. S. Packard, Jr., in connec- 
tion with the more directly practical labors of the U. S. Entomo- 
logical Commission, and it is to the kindness of Dr. Packard that 
I owe the opportunity of utilizing my observations for this 
article. ; 
I will merely remind the reader that the anatomy of the locust 
may be most readily understood by saying that its body is 
formed by an outer wall, including the external crust and the 
underlying muscles, and an internal tube, the digestive canal, the 
diameter and course of which are very irregular, as is shown in 
Fig. 1 of the accompanying plate. Between the body walls and 
the alimentary canal there is a large cavity in which various 
internal organs, notably those of circulation, respiration, and 
reproduction are situated. 
` Now, all these parts are composed of minute cells, and the 
examination of almost any one of them will suffice to show cells 
that are very characteristic. Let us take for instance a male 
grasshopper. The sexes may be readily distinguished by the 
position of the claspers at the end of the abdomen, which is 
straight in the female, while in the male it is curled upwards, so 
that the end of the abdomen appears club-shaped and the claspers 
seem placed on the back. 
Opening the insect along its back, and spreading out the sides 
So as to expose the internal organs, almost the first things that 
Strike the eye are the numberless glistening silvery threads, the 
ramifications of the tracheal tubes. These must be torn asunder 
in order to lay bare the reproductive organs, which form a large 
mass overlying the stomach in the anterior part of the abdomen; 
trace these organs downwards, following them around the sides 
of the intestiné to the ventral and posterior part of the abdomen, ; : 
and there will be found numerous long white tubes; these are the 
