1880. ] Development of Amphioxus lanceolatus. 95 
fers from other vertebrates. Beginning with the external character- 
istics we find a median ventral fin, which is continuous with a 
long median caudo-dorsal fin, extends. for some distance in front 
of the anal aperture, and which extends quite to the anterior ex- 
tremity of the body; an anal aperture placed upon the left side 
of the median line of the body and opening about midway of 
the side ; an abdominal aperture or branchiopore ; a longitudinal 
mouth opening; a circlet of mouth tentacles; and a single 
asymmetrical nasal pouch. It is very questionable whether the 
anterior pigment-spot of the spinal cord is of any more value 
than any of the other pigment spots of the nervous system, hence 
Amphioxus may be said to absolutely lack both eyes and ears. 
Internally we find a saccular liver; and an alimentary tract 
lined with vibratile cilia. The notochord, besides lacking any 
anterior cranial expansion, may differ in its structure and mode 
of development from the notochord of higher vertebrates, but 
this question is as yet undecided. The remaining organs repre- 
sent rather embryonic forms of the same organs in higher animals, 
than different features; thus the spinal cord, with its slight ante- 
rior enlargement seems to represent that stage of the central ner- 
vous system of higher vertebrates just before the cerebral vesicles 
are formed; and the blood system, if, as Langerhans claims, there 
is a heart, and if the blood is distributed throughout the body 
and returned to the ventral tubular vessel through the spaces in 
the tissues, rather than through capillary vessels, would be, except- 
ing the position of the heart and the pulsatile character of the 
vena cava, simply what is seen in all young vertebrates, or at least 
as seen in the young of osseous fishes, where the course of the 
blood in the smaller channels is continually changing from one 
interspace to another, whenever, from any cause, any one channel- 
becomes stopped up, and these changes continue until the capil- 
lary vessels are formed. Amphioxus is thus seen to be avery 
peculiar animal, presenting some resemblance to the Tunicates 
in the ciliated pharynx and pharyngeal tentacles, yet evidently 2 
more closely affiliated as an embryonic form, with the great 
Vertebrate branch of the animal kingdom, than with any of the 
Invertebrata. eer 
