MONILIGASTER GRANDIS, A. G. B. 351 
trunk, to find them acting as veins. This theory is borne out 
by observations on the development of a large Perichete. I 
do not find any stage in which commissural vessels run in 
each segment from the dorsal vessel to the ventral ; the hearts 
develop as such vessels, but in all the segments, those contain- 
ing the hearts as well as the others, a pair of dorso-tegumentary 
and a pair of ventro-tegumentary vessels develop and com- 
municate only through capillaries, so that at this stage the 
ventro-tegumentary vessels are the arteries of the peripheral 
tissues, and the dorso-tegumentary vessels the veins. This is 
a worm which, like all Perichetez, subsequently develops 
intestino-tegumentary vessels. 
Notes on the Clitellum and Generative Organs. 
Clitellum.—Beddard (13) has figured the structure of the 
clitellum and insists upon its being composed of ‘‘a single 
layer of cells,” by which I presume he means that none of the 
-cells dip down into the body-wall further than others, but 
they do so to a certain extent in his figure, and they do so to 
a great extent in all the clitella which I have examined, and 
I expect that the clitellum of his specimen of M. bahamensis 
was not fully developed. 
Even in the most fully-developed clitella which I have exa- 
mined, a number of the cells remain unglandular between those 
which have become glandular, a state of things which does not 
appear to occur in other earthworms. 
Generative Organs.—The resemblance of these organs 
to those of various lower Oligocheta is, as has been fully 
pointed out, very striking. My observations all tend to con- 
firm the resemblance. 
The ciliation of the speym-ducts is a very striking feature. 
The testes undoubte: y belong to Segment 1x. I may 
anticipate my observations on the development of the genus 
by stating that these organs develop as proliferations of the 
celomic epithelium of the anterior face of Septum 1x-x, and 
the ovaries as precisely similar structures on the posterior 
