94 Observations upon the Habits, Structure and | February, 
function as a cloacal chamber, although indeed receiving the 
urinary and generative products, I have thought it best.to give it 
the name of branchium rather than that of atrium, which is 
applied to the branchio-cloacal chamber of Tunicates. 
The changes which take place in the nervous system while 
these transformations are taking place in the muscular system 
and integument, appertain chiefly to the growth and extension of 
the nerves out into the parts of the body from the chorda spinalis. 
The chorda itself changes very little in the growth of the animal 
from what it was in the embryo; the principal difference being 
that in the adult the central canal has become almost completely 
filled up, except in the “head,” by the thickening of the walls, 
and the pigment spots are perhaps somewhat larger and more 
numerous. The posterior extremity is turned up very slightly 
from a very early period, but it does not exhibit the button-like 
termination until later in life. The anterior end, or “head,” 
enlarges somewhat in the growth of the animal, so as to repre- 
sent a very rudimentary brain, and the beak of the “head” and the 
olfactory nerve attain their adult characteristics probably coinci- 
dentally with the outward extension of the peripheral portion of 
the nervous system, or the general body nerves. 
The farther development of Amphioxus has already been indi- 
cated in the forward growth of the liver, the multiplication and 
elongation of the branchial slits, the outgrowth of the ventral car- 
tilaginous processes, forming a base to the ventral median fin, 
and the extension of the muscle plates down into the body walls. 
With these transformations are associated certain changes in 
external form, particularly in regard to the shape of the two ex- 
tremities and the appearance of the metapleura of the side folds, 
and when these are accomplished, the animal has assumed its 
adult form, as represented in Fig. 1, Pl. 1, and with the develop- 
ment of the generative bodies along the edges of the muscle 
plates, becomes capable of reproducing its kind. 
In conclusion, it may not be unprofitable to summarize, some- 
= what hastily, those particular features in which Amphioxus dif- 
terior portion of the animal, and while extending to the cloaca and opening there, 
include in their cavities the reproductive organs, then this posterior cavity would 
represent a true perivisceral cavity or chizoceele. In this case the anterior portion 
of the folds, forming after the posterior portions, and either from them or in front of 
them, would be true opercula covering the branchia, and it is possible that the growth 
or formation of ae body cavity and — in vertebrates has been along some a 
; such line of s diia a 
