440 Dr . Johnson's observations on the genus planaria. 
however remark, that the body consists of one common 
cavity, with diverging lateral cells or branches, destined to 
contain the nutriment ; being in this arrangement very analo- 
gous to the stomach of the medicinal leech. 
In the absence of food, the inter anea of these animals cannot 
be distinctly seen. In the P. lactea , they present a beautifully 
arborescent appearance, as delineated, highly magnified, in 
fig. 17. Sometimes they are of a deep purple colour, at other 
times of a brilliant red or dark brown, depending upon the 
nature of the food taken. 
The ventral apertures, which are two in number, and cir- 
cular, are very evident in each of the Planarice above de- 
scribed, but more particularly so in the P. torva ( fig. 6 ) ; the 
upper orifice gives passage to a long flexible tube, the lower 
one conducts to the ovarium. Of the use of this tube, which 
the Planarice frequently project, and which nearly equals the 
body in length, I remained for some time ignorant, when it 
was discovered to me by mere accident. 
Being desirous of ascertaining the proper food of these 
animals, as they were languishing in confinement, I threw in 
among them a variety of aquatic insects, worms, &c. One of 
them (P. cornuta ), after the lapse of a few minutes fastened 
upon a worm, immediately projecting and affixing this tube : 
the worm being in this way closely retained, other Planarice 
came forward to its assistance, and thus completely over- 
powered it. It is astonishing with what obstinacy they main- 
tained their hold, notwithstanding the writhings and contor- 
tions of the worm to effect its escape. 
The Planarice seldom attack the worm openly, seemingly 
aware of the difficulty of thus overcoming it, but seize upon 
