140 
ZOOLOGY. 
brain* and spinal cord, but sends off a few nerves to tLc 
periphery, with nerves to the two minute eye-spots. There 
are no kidneys like those of the higher Vertebrates, but 
glandular bodies which may serve as such. The reproductive 
glands are square masses attached in a row on each side of 
the walls of the body-cavity. The eggs may pass out of the 
mouth or through the pore. Kowalevsky found the eggs 
issuing in May from the mouth of the female, and fertil- 
ized by spermatic particles likewise issuing from the mouth 
of the male. The eggs are very small, 0.105 millimetres 
in diameter. The eggs undergo total segmentation, leav- 
ing a segmentation-cavity which becomes the body-cavity. 
The blastoderm now invaginates and the embryo swims 
about as a ciliated gastrula. The body is oval, and the 
germ does not differ much in appearance from a worm, 
star-fish, or ascidian in the same stage of growth. No ver- 
tebrate features are yet developed. 
Soon the lively ciliated gastrula elongates, the alimentary 
tube arises from the primitive gastrula-cavity, while the 
edges of the flattened side of the body grow up as ridges 
which afterwards, as in all vertebrate embryos, grow over 
and enclose the spinal cord. When the germ is twenty-four 
hours old it assumes the form of a ciliated flattened cylin- 
der, and now resembles an Ascidian embryo, there being a 
nerve-cavity, with an external opening, which afterwards 
closes. The notocord appears at this time. 
In the next stage observed the adult characters had ap- 
peared, the mouth is formed, the first pair of gill-openings 
are seen, eleven additional pairs appearing. It thus appears 
that while the lancelet at one time in its life presents 
Ascidian features, yet, as Balfour states, ^^all the modes of 
development found in the higher Vertebrates are to be 
looked upon as modifications of that of Amphioxus.^^ 
* Langerhans has figured an olfactory lobe; and all observers 
agree that a yentricle is present; thus there is a slight approximation 
to a brain. 
