In accordance with this view there would be also some probability in favour of regarding the collar nerve-tube of the Enteropneusta as the equivalent of the cerebral vesicle only of Amphioxus and the Ascidian tadpole, and also of the primary forebrain of vertebrates.
The ordinal name for the genera and species of Amphioxus is Cephalochorda, the term referring to the extension of the primary backbone or notochord to the anterior extremity of the body; the family name is Branchiostomidae.
While in Amphioxus the tb, tongue-bars.
With regard to its habits, all that need be said here is that while Amphioxus is an expert swimmer when occasion requires, yet it spends most of its time burrowing in the sand, in which, when at rest, it lies buried with head protruding and mouth wide agape.
Alimentary, Respiratory and Excretory Systems. - Although the function of the two latter systems of organs is the purification of the blood, they are not usually considered together, and it is therefore the more remarkable that their close association in Amphioxus renders it necessary to treat them in common.
It is important to emphasize the fact that in Amphioxus the excretory tubules are co-extensive with the gill-clefts.
One point must not be omitted, namely, the homogeny of the endostyle of Amphioxus and the thyroid gland of Craniata.
Of these, the former includes two subgenera, Amphioxus (s.
The development of Amphioxus possesses many features of interest, and cannot fail to retain its importance as an introduction to the study of embryology.
Although it is true that there is a certain amount of gradation in the degree of development to which these organs have attained in the various orders, yet it is hardly sufficient to enable the imagination to bridge over the gap which separates Amphioxus from the lowest fishes in regard to this feature of organization.