PULSATIONS IN THE AORTIC ARCHES OF THE 

 EARTHWORM. 



BY M. E. MANN. 



Anyone working with the common earthworm has probably 

 noticed the extreme irritability of the animal at the touch of 

 the hand, due to the rapid evaporation from the delicate cuticle 

 surrounding the worm. Observing also that the pulsations in 

 the aortic arches increased with the irritability, a few experi- 

 ments were tried to note the effect of temperature upon the pul- 

 sating arches of the common worm.- 



In the lowest animals the nutrient material resulting from 

 digestion is distributed in the same manner as in the cell. 

 The simplest form of a vascular system is found in the 

 Coelenterates, in which the digestive cavity occupies nearly 

 the entire space of the animal, and thus distributes the nutrient 

 material. 



When a distinct alimentary tract is developed, the nutrient 

 fluid passes through the walls of the tract, into the coelum, and 

 thus gives rise to the fluid, the blood. In this space the blood 

 circulates, the movement being effected chiefly by the muscular 

 actions of the body walls. 



At a higher stage, a rudimentary central organ of circulation 

 appears, and the nutrient fluid is confined in special pulsating 

 -vascular trunks, by means of which the fluid is forced through 

 the system. 



In the common earthworm a completely closed vascular 

 system is present, provided with pulsating trunks. A dorsal 

 longitadiuai trunk, and a central longitudinal trunk can be dis- 

 tinguished, the two being connected iu the anterior end by 



