PLEUROBRACHIA RIIODODACTYLA. 



33 



point of attacliniont, and the peculiar abactinal system (Fig. 4S) has 

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



Fig. 49. 



Fig. 60. 



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 sui'face of the ambulacral tubes (Fig. 49). 



The diflerence between the 

 axes, the coehac and the dia- 

 coeliac, grows less and less with 

 advancing age, till they assume 

 the almost identical outlines of 

 the adult, as seen in Fig. 50, 

 which repi'esents 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 l)ulb, and there are at 

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



Greenland (Fabricius) ; New England (Agassiz). 



Cat. No. 3GG, Nova Scotia, Anticosti Expedition, 18G1. 



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



Fig. 48. Somewhat loss advanocil than Fii^. -4 7, showing the lateral tubes from the iiaiTow 

 side, as a prolongation of tlie anihnlacral cavity. 



Fig. 49. Plenrol)raehia aliont in condition of Fig. 4 7, seen from aetinal pole. 

 Fig. 50. Adnlt I'leurolirachia, from the head an<l narrow side, natural size. 

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

 KO. II. O 



