DEVELOPMENT OF THE LANCELET. 407 
chial sacs of Ascidians and of Balanoglossus. The water 
which enters the mouth passes out through these slits where 
it oxygenates the blood, and enters the peribranchial cavity, 
thence passing out of the body through the abdominal pore. 
(Fig. 387, c). The pharynx leads to the stomach (e), with 
which is connected the liver or cecum (jf). There is a 
pulsatile vessel or tubular heart, beginning at the free end 
of the liver, and extending along the underside of the phar- 
ynx, sending branches to the sac and the two anterior branches 
to the dorsal aorta. ‘‘On the dorsal side of the pharynx the 
blood is poured by the two anterior trunks, and by the 
branchial veins which carry away the aérated blood from 
the branchial bars, into a great longitudinal trunk or dorsal 
aorta, by which it is distributed throughout the body.” 
(Huxley.) There are also vessels distributed to the liver, 
and returning vessels, representing the portal and hepatic 
veins. ‘The blood-corpuscles are white and nucleated. 
The vertebral column is represented by a notochord which 
extends to the end of the head far in front of the nervous 
cord ; and also by a series of small semi-cartilaginous bodies 
above the nervous system, and which are thought to repre- 
sent either neural spines or fin-rays. The nervous cord lies 
over the notochord ; it is not divided into a true brain* and 
spinal cord, but sends off a few nerves to the periphery, with 
a nerve to the single minute eye. 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 sidé 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 fertilized by sper- 
matic particles likewise issuing from the mouth of the male. 
The eggs are very small, 0-105 millimetres in diameter. The 
eggs undergo total segmentation, leaving a segmentation- 
cavity. The body-cavity is next formed by invagination. 
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, starfish, 
* Langerhans has figured an olfactory lobe; and all observers agree 
that a ventricle is present ; thus there is a slight approximation to a 
brain. 
