1880. | Development of Amphioxus lanceolotus. 83 
and a large one from its left side. The anterior vessels proceed 
to and supply the walls of the buccal cavity and the tentacles, 
‘and the left branch, which forms the ductus Botalli, or aortic 
arc, passes across the pharynx between the pharyngeal ring 
and the anterior branchial clefts, to unite with the left aorta, 
formed by the union of the left branchial vessels, and by this 
route sends its blood into the main arterial channel. 
The blood of Amphioxus is colorless, containing only white 
nucleated corpuscles, and very few of these. The manner, how- 
ever, of its distribution from the aorta and branches of the heart 
to the different parts of the body and its return to the vena cava 
and heart is not at present known. It may be that the passage 
is effected by means of capillary vessels which are so minute that 
they have not as yet been made out, or it may be, and which is 
much more probable, that this fluid passes through the inter- 
Spaces between the various tissues, or in other words, that the 
large blood vessels terminate as blood sinuses. 
Development.—F or those changes which take place in the em- 
bryo of Amphioxus previous to the formation of the side folds, and 
for most of my information in regard to the growth of these folds, 
I am chiefly indebted to the investigations of Kowalevsky? who 
has shown that shortly after the impregnated ovum leaves the 
branchium of the female and passes into the surrounding water, 
the granular vitellus, which nearly fills the rather delicate vitel- 
line membrane, undergoes complete segmentation and gradually 
builds up a thin-walled, nearly spherical morula, which soon, 
under the energetic action of the numerous external vibratile 
cilia, each cell of the wall being furnished with one or more 
of these little lashes, begins rolling over and over, quite slowly, 
Within the enclosing membrane, agreeing in this respect with 
what is seen in the ova of certain other vertebrates and many of , : 
the invertebrata. After the commencement of these rotary a 
movements, or it may be before they begin, the morula be- 
comes transformed, by the introversion of one side and the sul = 
sequent near approximation of the edges of the cup thus pro- 
duced, into a gastrula, and the gastrula, by the elongation of its oe 
phe Examination of the corpuscles of ‘the blood of Amphioxus lanceolatus. Prof. t 
L3 nga ey. Report of Brit. Ass. of. Science. London, aea Report of sections, 
iba, cit, and Weitere Studien über die EE E Jes Amphio ina 
opema Archiv, für Mik. Anatomie, xu r 181. Tae on 
