bo 
2 
ANATOMY AND PHYSIOLOGY I 
intima is penetrated by fine pore canals through which the 
secretion passes. In many insects, notably the cockroach, the 
common duct is held distended by 
spiral threads which give the duct 
much the appearance of a tra- 
chea. 
Fic. 154. 
In herbivorous insects the saliva 
changes starch into glucose, as in 
vertebrates; in carnivorous forms it ” 
acts on proteids and is often used 
to poison the prey, as in the larva 
of Dytiscus. In the mosquito each 
gland is three-lobed (Fig. 155) ; the istelogy or seakvarye plead 
middle lobe is.different-in appearance 0% C@silius, radial section. 0, 
basement membrane; c, canal; 
from the two others and secretes  ¢g, glandular cell; i, intima; 1, 
: : : : Z nucleus.—After Ko.se. 
a poisonous fluid which is carried out 
along the hypopharynx. Though this poison is said to facili- 
ate the process of blood-sucking by preventing the coagulation 
tate the | f blood-sucking by preventing the coagulatio 
of the blood, its primary use was perhaps to act upon proteids 
in the juices of plants. 
Malpighian Tubes.—The kidney, or Malpighian, tubes, 
present in nearly all insects, are long, slender, blind tubes open- 
ing into the intestine imme- 
Fic. 155. 
diately behind the stomach 
as.a tule (Figs. 145, 146). 
but always into the intestine. 
One of the three-lobed salivary glands he number of kidney tubes is 
of a mosquito. The middle lobe secretes a: We Cree : es - 
the poison.—After Mactosxiz, from the VElry different in different in- 
Se ae Se sects; Collembola have none, 
while Odonata have fifty or more and Acridiidze as many as 
one hundred and fifty; commonly, however, there are four or 
six, as in Coleoptera, Lepidoptera and many other orders. 
Not more than six and frequently only four occur in the em- 
bryo (Wheeler), though these few embryonic tubes may sub- 
sequently branch into many. 
