238 The American Naturalist. [March, 
in a higher class of the Vermes, which are furnished with both 
dorsal and ventral vessels, with pairs connecting them at regular 
intervals. One or more of these transverse vessels may be 
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FIG. 1.—Diagram of the vascular a of Nemer- 
tina : Pr dorsal longitudinal trunk ; 7, lateral Seng 
The arrows indicate the direction of the stream of 
blood. After Gegenbaur. 
—Vascular system of Senuris variegata : 
rsal vessel ; v, ventral vessel; c, heart-iike en- 
large ment of a transverse. The e arrows indicate the 
direction of the current of blood. After Gegenbaur. 
enlarged and pulsatile. 
While at other times the 
dorsal vessel itself acts 
as a heart. In this last 
we are to trace the origin 
of the heart of both an- 
thropods and vertebrates. 
In the one great group, 
the Mollusca, there are 
four types whose sevefal 
hearts furnish as clear a 
demonstration of the evo- 
lution of an organ as 
could well be desired. 
Some reader, unacquain- 
ted with comparative 
anatomy, may even 
imagine the sketch (Fig. 
3) an ideal one by some 
over-zealous evolutionist, 
made to confirm his 
theory; but myriads of 
these hearts are throbb- 
ing to-day as living con- 
tradiction to this sus- 
picion. A represents a 
dorsal vessel and trans- 
verse trunks of the worm, 
such as we have already 
s.enin Figs. 1 and 2. 2. 
Here we have the single, 
straight, pulsating ven- 
tricles (v) with the branching auricles (a), as found in the Nautilus. 
In C we have a similar organ of the Loligo, with the auricles 
— 
