ENDOSTYLE. 



43 



the rest and forms the perigonadial coelom which lies in the 

 outer wall of the atrium (Fig. 10). 

 The club-shaped gland and endostyle. The club-shaped gland 



B 



FIG. 30. A, B, C. Three side views of the ventral end of a niyotome of a young Amphipxus, 

 showing the development of ihf genital rudiment and its projection into the cavity of 

 the preceding somite (from Korschelt and Heider, after Boveri). 



is developed as a transverse groove on the floor of the pharynx 

 and continued on to the right and left walls. It becomes con- 

 stricted off from the pharynx, and acquires an opening to the 

 exterior on the left side of the body just in front of the mouth. 

 Later on the right end of it acquires an opening into the pharynx. 

 The club-shaped gland is of unknown function and eventually 

 atrophies. It has been suggested 

 without any obvious justification 

 that it is the metamorphosed an- 

 terior gill of the right side. 



The endostyle is a ciliated tract 

 of columnar epithelium just an- 

 terior to the club-shaped gland 

 on the right side (Fig. 24). It 

 subsequently becomes bent on 

 itself in a V-shaped manner 

 (Fig. 25), and grows backwards 

 between the two rows of gill- 

 slits. It is at first, therefore,' on 

 the right side of the body, but 

 when the larva becomes sym- 

 metrical, it takes up its position 

 in the ventral middle line. 



From the above account it is 

 clear that in the young larva 



-bni 



FIG. 31. Transverse section through 

 the genital rudiment of a young 

 Amphioxus showing the separation 

 of the perigonadial coelom from 

 the myocoele. bm ventral muscle; 

 g blood-vessel ; gd gonad ; w fold 

 separating myocoele from peri- 

 gonadial coelom. 



