134 



DEVELOPMENT OF AMPHIOXUS. 



low the mouth (see Fig. 64), the club-shaped gland has 

 now acquired an opening at its upper extremity, on the 

 right side, into the pharynx. 7 The gland lies, as usual, 

 behind, and closely approximated to, the endostylar tract, 

 which is bent forwards on itself at its upper end (Figs. 75 

 A and B\ 



Pigment-spots are present in great numbers at the base 

 of the neural canal. The pigment is deposited in special 



~fc 



Jt,.C 1 



a.r.m. 



Fig. 76. Transverse sections through the region of the prasoral pit. (After 

 LANKESTER and WILLEY.) 



A. Through a larva, with twelve gill-slits and no atrium. 



B. Through a larva, in which the atrium was closed in over all the gill-slits 

 except the first two. (Cf. Fig. 38 C.) 



a.r.m. Anterior median portion of right metapleur. p.o.c. Prasoral body-cavity 

 (right head-cavity) ; this cavity becomes much reduced after the metamorphosis, 

 and is largely filled up by gelatinous tissue, p.p. Praeoral pit. s.o. Sense-organ 

 of prceoral pit (groove of Hatschek). l.o.h. Rudiment of left half of oral hood. 

 my' . Sclerotome (diverticulum of myoccel my). Other letters as above. 



Section B is taken through a plane slightly posterior to section A. 



