STRUCTURE OF AMPHIOXUS 



525 



ten to thirty-five on each side (Fig. 295, G.). Each Ues in 

 a " genital chamber " formed in development by constric- 

 tion from the cavity of the myotome. 



In the mature female the ovaries are large and con- 

 spicuous ; the ova burst into the atrial cavity, whence they 

 pass out by the atriopore. 



The testes are like the ovaries ; the spermatozoa burst 



Fig. 300. — Small portions of excretory organs of Amphioxus (A) 

 and the Polychaete Phyllodoce (B). — After Goodrich. 



S., Solenocyte ; N., nucleus ; FL., flagellum ; T., tube ; EC, excretory canal. 



into the atrial cavity, and pass out by the atriopore. The 

 eggs are fertilised in the surrounding water. 



Development. — The fertilised ovum is about ^^ in. in 

 diameter. The segmentation is complete and almost equal 



is cut through along its line of insertion. The result is to show 

 that the chamber is prolonged dorsally into a series of bays {b.), 

 which lie on the surface of the tongue-bars {t.b.). Into these 

 bays each of the nephridia {n.) opens by a pore (o.), while they 

 also project internally by blind funnels (/.), fringed by very 

 large solenocytes (c.)- The bays are separated by ridges [d.), 

 formed by a downgrowth of the walls of the coelom over the primary 

 bars {p.b.). my., A myotome ; sy., one of the synapticula con- 

 necting the pharyngeal bars. 

 The lower figure is a more superficial view, to show the blood vessels 

 which form an anastomosing plexus (c.) over the walls of the 

 nephridia (nph.). d., Dorsal aorta ; coe., coelomic space within 

 primary bar ; b.v., blood vessel of secondary bar ; m., cut edge 

 of the wall of the atrial hamber ; other letters as before. 



