36 



MARINE ANIMALS OF MASSACHUSETTS BAY. 



with its rapid gyrations, its short ambulacra! tubes, like immenso 

 pouches (Fig. 37), its large pigment spots scattered over the sur- 

 face (Fig. 38), was an earlier stage of the rosy-hued Idyia, which 

 glides through the water with a scarcely perceptible motion. 



Fie. 38. 



Fig. 39. 



Fig. 40. 



Figs. 37-40 represent the various stages of its growth. It will 

 be seen how very short are the locomotive fringes (Fig. 39) in 

 comparison with those of the full-grown ones (Fig. 33). It is 



only in the adult Idyia that these rows 

 attain their full height, and the tubes, 

 ramifying throughout the body (Fig. 

 40), are completed. 



The Bolina, in its early condition, 

 recalls the young Pleurobrachia. 

 At this period it has the same rapid 

 motion, and when somewhat more 

 advanced, long tentacles, resembling 

 those of the Pleurobrachia, make 

 their appearance (Fig. 41) ; it is only 

 at a later period that the tentacles 

 become contracted, while the large 

 lobes (Fig. 42), so characteristic of 



Bolina, are formed by the elongation of the oral end of the 

 body, the auricles becoming more conspicuous at the same 



Fig. 38. Young Idyia seen from the anal extremity, magnified 5 a anal opening, other letters as in 

 Fig. 36. 



Fig. 39. Idyia somewhat older than Fig. 37, lettering as before ; magnified. 



Fig. 40. Young Idyia in which the ambulacral tubes begin to ramify ; magnified, letters as before. 



