14 T. H. MORGAN. 



After these changes have taken place we reach a stage shown 

 by Figs. VII and VIII. The first figure is a ventral view of the 

 embryo at a time when it is ready to leave the parent. The three 

 pairs of segmented walking legs have become straightened out at 

 the sides of the body. In the figures only the proximal ends 

 are shown. The fourth pair of walking legs appears at the pos- 

 terior end of the body. The first pair of appendages — the cheli- 

 cerge — are now attached quite dorsally to the proboscis, which 

 appears between and below them. Each has three segments, 

 including the terminal one, which acts together with the second 

 to form the pincers. On the sides of the body, just in front of the 

 first paif of ambulatory legs, are a pair of projections, one on each 

 side. These are the beginnings of the third pair of limbs — the 

 ovigerous legs. I have seen no traces of the second pair of 

 appendages in the ontogeny of Pallene. Five pairs of large 

 ganglia lie along the body, and in addition a small sixth pair. 

 The first pair, as we have seen, is double, and composed of the 

 first and second pairs. The next pair, the third, is between the 

 first pair of ambulatory legs; the fourth pair of ganglia lies 

 between the second pair of legs; the fifth near the base of the 

 third pair of legs, and the sixth, each of whose ganglia are smaller 

 than those in front, at the base of the fourth pair of legs. The 

 small, seventh pair of ganglia belongs to the rudimentary 

 abdomen, and does not lie in a plane with the more anterior 

 ones, but, like the sixth, is dorsal to the one in front of it, as 

 partially shown in the figures. The oesophagus is seen to start 

 at the distal end of the proboscis and to disappear in the body, 

 where it is not easily followed on account of its transparency. 

 The prolongation of the mid-gut into the legs is not shown in 

 the figures, except for the last pair of immature legs. 



In Fig. VIII is a dorsal view of the same embryo. Four pairs 

 of large ventral ganglia are seen, and in addition the small rudi- 

 mentary ganglia of the abdomen. The fused first and second 

 pairs are hidden by the brain. On the surface of the brain are 

 seen four small pigmented eyes. The oesophagus is triangular 

 in shape in cross-section, with the broad base turned upwards, 

 and this base is seen from the surface. At the posterior end of 

 the animal the rudimentary abdomen is seen, and at its end is 

 the opening of the anus. 



