wists or coils straight to the anus, which is situated at the
junction of the trunk with the tail. A median mesentery running
dorso-ventrally supports the alimentary canal and is continued behind
it into the tail, thus dividing the body cavity into two lateral
halves.

There are no specialized circulatory, respiratory or excretory organs.

The nervous system consists of a cerebral ganglion in the head, a
conspicuous ventral ganglion in the trunk, and of lateral commissures
uniting these ganglia on each side. The whole of this system has
retained its primitive connexion with the ectoderm. The cerebral
ganglion also gives off a nerve on each side to a pair of
small-ganglia, united by a median commissure, which have sunk into and
control the muscles of the head. As in other animals there is a minute
but extensive nervous plexus, which permeates the whole body and takes
its origin from the chief ganglia. In addition to the eyes and the
olfactory circle on the head scattered tactile papillae are found on
the ectoderm.

Chaetognatha are hermaphrodite. The ovaries are attached to the side
walls of the trunk region; between them and the body wall lie the two
oviducts whose inner and anterior end is described as closed, their
outer ends opening one on each side of the anus, where the trunk joins
the tail. According to Miss N.M. Stevens the so-called oviduct acts
only as a "sperm-duct" or receptaculum seminis. The spermatozoa enter
it and pass through its walls and traverse a minute duct formed of two
accessory cells, and finally enter the ripe ovum. Temporary oviducts
are formed between the "sperm-duct" and the germinal epithelium at
each oviposition. A number of ova ripen simultaneously. The two testes
lie in the tail and are formed by lateral proliferations of the living
peritoneal cells. These break off and, lying in the coelomic fluid,
break up into spermatozoa. They pass out through short vasa deferentia
with internal ciliated funnels, sometimes an enlargement on their
course--the seminal vesicles--and a minute external pore situated on
the side of the tail.

With hardly an exception the transparent eggs are laid into the sea
and float on its surface. The development is direct and there is no
larval stage. The segmentation is complete; one side of the hollow
blastosphere invaginates and forms a gastrula. The blastopore closes,
a new mouth and a ne