1880. ] Development of Amphioxus Lanceolatus. II 
said to represent spinous processes, which extend along nearly 
the entire length of the dorsum, and along the ventral side of the 
tail portion of the animal; and a series of arches or supports 
which are formed along and in the sides of the anterior half of 
the alimentary canal. The xotochord has already been described, 
and its position defined as forming an axial support extending 
from end to end of the body, and representing the back bone of 
higher vertebrates, but lacking the anterior expansion or brain 
case. The spinous processes form rows of semi-transparent, per- 
pendicularly placed, block-like bodies; the dorsal row origi- 
nating over the chorda dorsalis, and rising upwards from between 
the side muscles to form a median basal support to the dorsal 
fin; and the ventral row originating beneath the intestine and 
extending out from between the side-muscles to form a support 
to that portion of the median fin which extends from the branchio- 
pore back to the ventral “blade.” of the tail. These blocks are 
well marked, and form quite a prominent border to the greater . 
part of the outline of the muscular portion of the body. (Figs. 1 
and 5, Pl. 1, and Fig. 7, Pl. 11.) The series of bodies pertaining to 
the alimentary. canal consist of a mouth ring, a pharyngeal ring 
and a variable number of rib-like arches placed alternately upon 
either side of the canal and extending back to about the middle. 
of the body. These different parts are unconnected above, unless 
it may be toa slight extent with the sheath of the notochord, 
but below, the two rings, which arise from a common base, are 
connected with the arches by a cartilaginous trough-like forma- 
tion which extends back as far as the last arch, and in the sides 
of which the bases of the arches are firmly imbedded. The 
mouth ring is formed in the integument of the edges of the 
mouth orifice, and arches forward and upward in conformity to 
the outline of this portion of the body. It is made up of seg- 
ments, one for each tentacle, and each segment sends out from 
the side, at the anterior end, a long, slender prolongation which 
extends, as ‘a central support, to the very tip of its corresponding 
tentacle. (Fig. 2, Pl. 1.) These segments, which are the same in 
number upon both sides of the mouth, do not unite in front, but 
form arms which end upon either side just at the base of the ram- 
Aes entity of the body, and at these terminations of the 
“ring” new segments are formed, when, in the growth of the 
animal, there is room in the oral circlet for additional tentacles. 
