2 
rOPULAH SCIENCE KEYIEW. 
semigelatinous rod (ch) (the “notochord,” or chorda dorsalis of 
embryologists), enclosed in a membranous sheath (n) supporting 
the spinal cord ( md ). 
Fig. 1. 
DIAGRAM OF THE ANATOMY OF THE “ LANCELET,” AmpMoXUS , OR Branchiostoma 
(after Owen).* 
There is no skull, and the spinal cord do6s not expand in 
front to form a distinct brain or cerebrum . The body is lanceo- 
late in shape, and is provided with a narrow membranous 
border, of the nature of a median fin, which runs along the 
whole of the dorsal and a portion of the ventral surface, and 
expands at the tail to form a lancet-shaped caudal fin. No 
true 66 paired ” fins representing fore and hind limbs exist. The 
mouth (6) is a longitudinal slit, placed at the front of the head, 
entirely destitute of jaws, but surrounded by a number of oral 
cirri (/,/), which are borne by a pair of jointed cartilaginous 
filaments. The throat is provided with several leaf-like fila- 
ments (g, g ), which are richly supplied with blood, and appear in 
part to discharge the function of gills. The mouth opens into 
a dilated chamber, termed the pharyngeal or branchial sac (ph). 
The walls of this chamber are strengthened by numerous 
cartilaginous filaments (r, r, r), between which are transverse 
slits (ce) or clefts, not opening upon the skin, and the whole 
chamber is lined with a richly ciliated mucous membrane. 
The water admitted by the mouth passes through the bran- 
chial clefts into the abdominal cavity, and escapes through the 
aperture (as) in the ventral surface. The alimentary canal (i, i) 
proceeds from the posterior end of the branchial sac ; it has a 
sac-like organ (h) appended to it, which probably represents 
the liver. 
* We are indebted to the courtesy of Messrs. Longmans & Co. for per- 
mission to use this woodcut, and also for Fig. 2, from Prof. Owen’s “ Com- 
parative Anatomy, Vertebrates,” Yol. I., 1866, p. 31, fig. 23, and p. 26, fig. 16. 
Letters in woodcut, Fig. 1, not referred to in the text: — 
oh. longitudinal filamentary ligament supporting the spinal chord ; 
;/. posterior termination of notochord ; bv. branchial vein ; ba. branchial 
artery ; ov. ovarian vessel ? od. ovarian duct P h. the liver ? ltd. hepatic 
duct; \nj. pylorus. 
