182 AMPHIOXUS 



The ova, which measure ^^ inch in diameter 

 ultimately pass through the gill- slits into the pharynx, 

 and escape through the mouth ; or possibly through 

 the hyoidean apertures. 



2. The male. 



The testes are similar in structure and position to 

 the ovaries; and the spermatozoa, when ripe, are 

 discharged like the ova into the atrial cavity, from 

 which they escape by the atrial pore. 



III. EXAMINATION OF TEANSVEESE SECTIONS. 



Many points in the anatomy of Amphioxus are far more 

 readily determined by an examination of transverse sections 

 of the whole animal than by dissection. For this purpose an 

 entire specimen should be cut by means of a microtome, and 

 the sections mounted on slides in their proper sequence. It 

 is only necessary to examine in detail a few of the more 

 typical ones. 



A. Transverse Section through the Buccal Cavity. 



1. General characters. The dorsal surface is indicated by 



the laterally compressed dorsal fin : the ventral 

 surface by the mouth -opening, which is bordered at 

 the sides by the thickened lips ; within the buccal 

 cavity are usually seen sections of the tentacles. 

 About the middle of the section is the notochord, 

 and above this is the spinal cord. At the sides are 

 the myotomes, separated from one another by con- 

 nective-tissue septa. 



2. The skin consists of two layers. 



a. The epidermis is a single layer of short columnar 



cells, with a thick cuticle on their outer ends. 



b. The derails is a very thin layer of connective tissue, 



underlying and supporting the epidermis. 



3. The skeletal system, 



a. The notochord is slightly oval, its longer axis 

 being vertical. It is crossed by numerous wavy 



