16 



BOLINA ALATA. 



with age. (Fig. 4, which is Fig. 6 seen from abactinal side.) We soon 

 jjerceive in the young of this species changes of shape similar to those 

 to be described in Idyia and Pleurobrachia : the outhne becomes more 

 elongated ; the lateral tubes, at first sunple diverticula from the main 



ambulacral tubes {I, Fig. 5), extend to the level of the opening of the 

 mouth (Fig. 6). We can also trace a difference in the rapidity of 

 growth of the ambulacral tubes, but, contrary to what we find in 

 other genera, we observe the tentacular ambulacra are the most rapid 



in their growth. When 

 ^'«'- '^'s.T. they reach the bottom of 



the spherosome, they bend 

 towards each other (Fig. 

 7), and finally join (Fig. 8), 

 but have at present no 

 connection with the latr 

 eral tvibes near the mouth. 

 It will be noticed by the 

 figure {n, Fig. 8) that that 

 part of the spherosome 

 which contains the junc- 

 tion of the two lateral am- 

 bulacra (Figs. 9, n, 10), has a tendency to expand beyond the level 

 of the mouth ; this is the first appearance of the lobes of the adult 

 Bolina. This part of the spherosome increases rapidly in dimensions, 

 and we have a minute Ctenophore with well-marked lobes, like a 

 Bolina, and highly developed tentacles, hke a Pleurobrachia (Fig. 11). 

 StUl greater changes are yet to take place ; we soon perceive that 



Fig. 2. Bolina in state of Fig. 1, seen from the broad side. 



Fig. 3. Somewhat younger than Fig. 1, seen from the abactinal pole. 



Fig. 4. Young Bolina, seen from the abactinal side, somewhat older than previous figures. 



Fig. 5. Formation of lateral tubes in young Bolina. 



Fig. 6. Bolina in which lobes begin to appear, seen from narrow side, same state as Fig. 4. 



Fig. 7. Somewhat more advanced than Fig. 6, the tube c' not yet having formed the circuit ; 



seen from the actinal side. 



