8 T. H. MORGAN. 



so clearly seen on the right-hand ganglion, but traces of it were 

 seen here also. These structures I shall speak of as the Ventral 

 Organs ; and we shall come across them again in Pallene, where 

 they are worked out in greater detail. 



Pallene empusa. 



There is a great variability in the size of the eggs on the 

 ovigerous legs of the males. The average size of those which 

 seem to be normal eggs is .25 mm., but often bunches contain 

 one or more much smaller eggs, some of which seem to begin to 

 develop. These very small eggs are most probably immature 

 'and accidental. Although the eggs of Pallene are much larger 

 than in the preceding animals — having 125 times the volume — 

 yet the yolk is almost transparent, so that nuclear divisions of 

 the segmenting egg are easily seen from the surface. The adult 

 is remarkably transparent and consequently most difficult to see 

 as it rests quietly amongst the hydroids or sea-weeds. It seems 

 that the eggs have also adapted themselves for purposes of protec- 

 tion in thus becoming transparent. More or less time necessarily 

 elapses after the animals are collected before they can be exam- 

 ined, so that I have been unable to see the extrusion of the polar 

 bodies. 



The nucleus of the egg and its accompanying protoplasm 

 is extremely large and situated near the center of the egg. 

 Each division of the nucleus is accompanied by a division of 

 its surrounding protoplasm, so that in surface views it is impos- 

 sible to separate the one from the other. In the figures of Plate 

 III the darker masses in each cell indicate the position of the 

 nucleus and protoplasm, but for the sake of brevity I shall speak 

 of this simply as the nucleus. In the unsegmented egg the 

 nucleus is seen to elongate and to divide into two halves, and 

 this is immediately followed by division of the egg itself into 

 two parts. The first furrow divides the egg into two unequal 

 segments. Fig. A, Plate III, shows an egg after the first divi- 

 sion. Each segment contains a single nucleus. (Hoek has made 

 a different observation from this — see infra.) After this first 

 segmentation the segments flatten somewhat and remain so 

 during the resting period. The second division came in about 

 three-quarters of an hour (to an hour) after the first. The 



