190 



THREE CRUISES OF THE " BLAKE. 



Vb^/ 



I 



in S. pinnata, side by side in a single row, stretching vertically 

 across the whole width of the chain, and forming a thin ribbon, 

 which when floating is usually slightly coiled like 

 a tape. The zooids of the chain resemble S. Afri- 

 cana. This species was found from Cape Hatteras 

 as far north as the eastern extremity of George's 

 Shoal. 



The sudden arrival of innumerable Salpse on 

 our coast is most interesting. It is not unfrequent 

 for the northern species of Salj)a (Figs. 110, 111), 

 so common along the eastern coast from Cape 

 Hatteras to Cape Cod, to make its appearance in a 

 single night in such masses as to discolor the sea 

 for miles near the entrance of Narraoansett Bav, 

 and to remain swarming for a couple of months, 

 when it disappears as quickly and mysteriously as 

 it came. The explanation of this sudden inroad 

 is probably due to the fact, that during the time 

 they are sterile the solitary individuals remain at 

 some distance below the surface, but when they 

 begin to bud and form the chains they come near 

 the surface. It is easy to explain their abundance 

 then by the rapid development of the young 

 chains, which are formed, thrown off, and increase 

 in size with extraordinary rapidity. 



The pteropods and heteropods are by 

 far the most common pelagic forms of the 

 mollusca, the dead tests of the former be- 

 ing literally heaped up in beds on the 

 bottom of the sea in deep water. The 

 dredge often came up completely choked 

 with pteropod shells, showing what an 

 important part they play in building up 

 the deep-sea deposits by the decomposi- 

 tion of their tests. In former geological 

 Chdin, somewhat enlarged, pcriods, whcu there wcrc gasteropods 

 allied to pteropods like Bellerophon, of gigantic size, their 

 effect in forming bottom accumulations must have been still 



Fig. 111.— Salpa Caboti. 



