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.^ 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 



UK 



a..r:m a.Trm. 



Fig. 76. — Transverse sections through the region of the pr.soral pit. (After 



L.^NKESTER and WiLLEY.) 



A. Through a larva, with t^\'elve gill-slits and no atrium. 



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

 e.\cept the first two. (Cf. Fig. 3S C.) 



a.r.m. Anterior median portion of right metapleur. p.o.c. Pra^oral bodv-cavitv 

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

 and is largely filled up by gelatinous tissue, p.p. Prajoral pit. s.o. Sense-or^an 

 of prreoral 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. 



