54 



ZOOLOGY 



SECT. 



cavity, is supposed to have a sensory function, but this is very 

 doubtful. Lastly, the sensory cells on the cirri of the oral hood 

 give those organs an important tactile function. 



Reproductive Organs. The sexes are separate, but there is 

 no distinction, apart from the organs of reproduction, between male 

 and female. The gonads (Fig. 752, gon., Figs. 751, A, and 753, g.) 

 are about twenty-six pairs of pouches arranged metamerically 



B 



FIG. 758. Amphioxus lanceplatus. Segmentation of the oosperm. D, the four-celled 

 stage (C) from above ; 0, vertical section of H ; K, vertical section of the blastula stage /. 

 (From Korschelt and Heider, after Hatschek.) 



along the body- wall, and projecting into the atrium so as largely 

 to fill up its cavity. The inner or mesial face of each pouch is 

 covered by atrial epithelium pushed inwards by the growth of 

 the gonads ; within this, and completely surrounding the repro- 

 ductive organ, is a single layer of epithelium which is shown by 



