394 



CEPHALOCHOEDA 



[CH. 



the cavity of the lower division is termed the intercoelic mem- 

 brane (i.m. Figs. 190 and 196). 



mp 



FIG. 189. Diagrammatic transverse section through pharyngeal region of a 

 female Amphioxus. After Lankester and Boveri, from E. Hertwig. 



at. Atrial cavity, c. Dorsal coelom, separated from atrial cavity by the double- 

 layered membrane known as the lig amentum denticulatum. ch. Noto- 

 chord. d.n. Sensory nerve. e. Endostyle, below which is the 



endostylar coelom containing the ventral aorta. /. Fin-ray of dorsal 

 fin. g. Gonadic pouch containing ova. h.v. Hepatic vein lying in 



the narrow coelomic space which surrounds I, the liver or hepatic coecum. 

 La. Left aorta separated from the right aorta by the hyperpharyngeal 

 (epibranchial) groove. ly. Lymph-space. mp. Metapleural fold, 



containing a lymph-space, my. Longitudinal muscles of myotomes ; over 

 against the dorsal coelom these muscles are arranged verticairy, and form the 

 rectus abdominis of Schneider. n.t. Spinal cord. p. Pharynx. 



r. Nephridium. t.m. Transverse or subatrial muscles. v.n. Motor 

 spinal nerve, the fibres of which have the appearance of passing directly 

 into the muscle-fibres. N.B. The connective tissue (cutis, notochordal 

 sheath, etc.) and the coelomic epithelium are indicated by the black lines. 



