196 AMPHIOXUS. 



lying along the ventral edge of the anterior three- 

 fourths of the length of the animal. 

 Eemove kvo or three of the reproductive organs : put them 

 on a slide in a drop of glycerine : tease them, and examine 

 with a microscope. 



The ovary of the female consists of large rounded 

 and polyhedral ova, with large nuclei : cf. fig. 42. 



The testis of the male has a finely granular ap- 

 pearance : the spermatozoa, when ripe, consisting of 

 minute heads with long thread-like tails. 



8. The transverse muscles of the ventral body wall in the 



pharyngeal region are well seen, immediately ventral 

 to the reproductive organs. 

 Remove the reproductive organs of the right side com- 

 pletely, so as to expose the alimentary canal along its whole 

 length. 



9. The atrial cavity is the space surrounding the walls of 



the pharynx at the sides and below. It opens to the 

 exterior by the atrial pore. 



10. The alimentary canal runs nearly straight from mouth 



to anus : it consists of the following parts : 



a. The buccal cavity is the most anterior portion : the 



mouth opening into it below, is bordered by ten- 

 tacles, which increase in length from before back- 

 wards. 



b. The pharynx, which is in part concealed by the liver, 



forms about half the length of the alimentary 

 canal : it is crossed by close-set parallel lines, 

 oblique to the axis of the body, and marking 

 the positions of the gill-clefts ; these do not 

 quite reach either the mid-dorsal or mid-ventral 

 lines, where the wall of the pharynx is formed 

 by the epibranchial band and the endostyle 

 respectively. 



c. The oesophagus is a short narrow tube leading from 



