189 



Where are the Excretory Organs of Amphioxus situated ? 



Describe them. 



The paired nephridia, restricted to the region of the 

 pharynx, are situated in the dorsal wall of the atrium and 

 project into tho dorsal coelomic canals (dorsal coelome). 

 Each nephridium is a ciliated tubule ; one end opens into the 

 atrium, and the other end (in the coelome) is expanded 

 into several short blind funnels. On the funnels there are 

 groups of cells like knobbed stalks, the flame -cells or 

 solenocytes (of., flame-cell, page 91, Part II.). The stalk is 

 a fine tubule, which opens through the funnel wall into 

 the excretory canal, and within the tubule there is a long 

 vibratile flagellum, which arises from the protoplasm 

 surrounding the nucleus in the knob end. The flagella 

 project into the excretory canal. On the wall of each 

 nephridium there is a network or anastomosis of capillary 

 blood-vessels, which is connected with the dorsal ends of 

 the branchial vessels and the aorta. This vascular net- 

 work is the glomerulus. 



FIN RAY OF DORSAL FIN 



SPINAL CORD 



SKELETOGENOUS 



TISSUE 



ECTODERM 

 CONNECTIVE: TISSUE 



MYOTOME 



NOTOCHORD 



AORTA 



E PIPHARYNGE AL 



GROOVE 

 PHARYNX 



LYMPH SPACE 

 OF METAPLEURE 



MUSCLE OF 

 ATRIAL FLOOR 



ENDOSTYLE 



SUB-ENDOSTYLAR COELOME 



FIG. 35. Amphioxus. Transverse section through 

 pharyngeal region of body. 



Write a short Description of the Reproductive System of 



Amphioxus. 



The sexes are separate. The gonads (testes and ovaries, 

 are outwardly similar, cube-shaped, structurally simple) 

 and without ducts ; there is a row of 26 along each side 

 on the wall of the atrium at the lower ends of myotomes 

 10 to 35. Each gonad is enclosed in a coelomic sae, a 



