PLEUROBRACHIA RHODODACTYLA. 



33 



point of attachment., and the peculiar abactinal system (Fig. 48) has 

 also made its appearance. The young Pleurobrachia has now all the 



Fig. 48. 



Fig. 49. 



Fig. 50. 



appearance of the adult, only it is more pear-shaped, and it is about one 

 half of an inch in polar diameter. The ambulacra are yellowish, with large 

 orange pigment-cells on the surface of the ambulacra! tubes (Fig. 49). 



The difference between the 

 axes, the coeliac and the clia- 

 coeliac, grows less and less with 

 advancing age, till they assume 

 the almost identical outlines of 

 the adult, as seen in Fig. 50, 

 which represents the coeliac 

 and diacoeliac views of an adult. 

 In Figs. 47 and 48 we have 

 also the first trace of the cirri 

 which assume such graceful 

 shape in the tentacles of the 

 adult Medusa (Fig. 51) ; the 

 cirri begin nearest the tentac- 

 ular bulb, and there are at 

 first but two or three at the base of each tentacle. 



Greenland (Fabricius) ; New England (Agassiz). 



Cat. No. 366, Nova Scotia, Anticosti Expedition, 1861. 



Museum diagrams Nos. 4, 5, after L. Agassiz and Alex. Agassiz. 



Fig. 48. Somewhat less advanced than Fig. 47, showing the lateral tubes from the narrow 

 side, as a prolongation of the ambulacral cavity. 



Fig. 49. Pleurobrachia about in condition of Fig. 47, seen from actinal pole. 

 Fig. 50. Adult Pleurobrachia, from the head and narrow side, natural size. 

 Fig. 51. Adult Pleurobrachia in a natural attitude, natural size. 



5 



& 



NO. n. 



