192 



THREE CRUISES OF THE " BLAKE. 



the bathymetrical range of free-swimming animals like these. 

 Argonauta (Fig. 113) has been known for a long time to be 



Fig. 116. — Sagitta. ^. 



pelagic, while nautilus, though seen at the surface occasionally, 

 is probably a deep-sea type. Spirula has been dredged from 

 deep water by the "Challenger" and "Blake," while French 



Fig. 117. — Tomopteris. f. 



collectors have observed it swimminof in numbers at the sur- 

 face in the Indian Ocean. The shells of Spirula (Fig. 114) are 

 common on all tropical shores, while the shells of Argonauta 



