326 ALFRED GIBBS BOURNE. 
the extreme sluggishness of the hinder end of the worm, and 
to contrast this state of things with that which obtains in, 
for instance, M. ophidioides, M. robustus, and M. sap- 
phirinaoides, where, coexisting with a much more active 
body throughout its entire length, there is a much more 
definite connection between the subneural vessel and one of 
the posterior longitudinal trunks (fig. 29). 
There are no latero-neural vessels. 
It will be convenient to defer for the present the description 
of the various branches of this latero-longitudinal and subneural 
system. 
Hearts (figs. 27, 32, and 33).—There are four pairs of 
hearts, and these belong to Segments vi, vii, viti, and Ix. 
There is in some worms a little. difficulty in determining 
whether certain particular branches of the dorsal vessel should 
be regarded as hearts or not. In Moniligaster there is no such 
difficulty. In all the species which I have examined there are 
four pairs of hearts and four only. 
Their walls are so muscular that when spirit is poured upon 
a freshly-opened worm the walls of the hearts become so opaque 
that their red contents can no longer be seen, while the well- 
developed network of vasa vasorum (fig. 32) supplying their 
walls comes very clearly into view. The walls of the dorsal 
vessel also become opaque under similar conditions, only to a 
very much less degree. In no other vessels of the body are 
the contents in the least degree obscured by the action of the 
spirit, nor do I know any other worm in which this pheno- 
menon occurs to anything like the same degree, even in the 
hearts, as in Moniligaster grandis. 
The three anterior pairs of hearts are very simply connected 
with the dorsal vessel (fig. 32). There is a short narrow neck, 
and at the junction of this with the dilated heart there is a 
sphincter muscle. The hearts stand out well from the walls 
of the cesophagus, but each is attached to the wall along its 
whole length by a double fold of mesentery. 
The hearts of the most posterior pairs have necks at their 
upper extremities similar to those of the more anterior pairs, 
