148 THE AMPHIOXUS. 



especially since the widening of the wall as well 

 as of the central canal is very important (Figs. 122, 



123 and Figs. 129-132). 



At a quite definite place, in the fifth myotome in 

 the ventral wall of the medullary tube, a black pig- 

 ment spot makes its appearance at a fixed time (Fig. 

 54, etc). Much later, at the end of the embryonal 

 development, there appears also a pigment spot, which 

 unmistakably has the appearance of an eye spot. At 

 the end of the embryonal development the first nerve 

 fibre strands make their appearance in the neural canal 

 more exactly in the two ventral laterally drawn edges. 

 We will gain, a closer acquaintance with these later 

 on, when considering the larva. 



THE TRANSFORMATION OF THE ANTERIOR HYPOBLAST 



DIVERTICULA. 



For the formation of the anterior end of the body, 

 the destinies of those anterior evaginations of the 

 alimentary canal, which we saw originating at the 

 conclusion of the former period of development, are 

 of great importance. 



These evaginations, which appeared in pairs and 

 symmetrically, are further formed in a curiously 



