ABSTRACTS OF LECTURES. 63 



sum up, the conditions under which life here exists are 

 absolutely monotonous and invariable. 



Under such conditions we expect to meet new forms, but 

 are taken aback to find at the same time species closely allied 

 to inshore forms (e.g., Acti?iia tnesembryanthemum — shore, 

 A. abyssorum — 1,350 fathoms). All invertebrate groups, with 

 the exception of Planarians, Rotifers, Tardigrades, and 

 Infusorians, are represented below i,ooo fathoms. Many 

 genera and species have a wide range of depth, e.g. : — 



Terebratula vitrea, 5 to 1,456 fathoms. 

 Antedon, coast to 2,900 fathoms (Carpenter). 

 ■ Amphiura, 2 to 2,650 fathoms (Lyman). 

 Balanoglossus, coast to 2,500 fathoms (Ehlers). 

 Lumbriconereis fragilis, coast to 1,780 fathoms (Mcintosh). 

 Dentalium, coast to 2,600 fathoms (Watson). 

 Peneid and Caridid Shrimps to all depths. 

 Bathyactis symmetrica, 30 to 2,900 fathoms. 



Only typical deep-sea forms are closely confined. At the 

 same time the geographical range is unrestricted owing to 

 the even condition of the sea-bed. Thus some forms are 

 found universally, e.g., the hydroid, Cryptohelia. Agassiz 

 has found off the American coast most of the species dredged 

 by the " Challenger " throughout her voyage. There is a 

 close connection between deep and surface forms. We find 

 surface Rhizopods, Hydroids, Bryozoa, and Barnacles with 

 corresponding forms below. Some even live at the surface 

 when young, and descend later e.g. Himantolophus, a fish of 

 the angler type. 



Turning to true characteristic deep-sea forms we find 

 great morphological changes resulting from the peculiar 

 physical conditions of life. In the absence of sunlight 

 phosphorescent organs are highly developed. They may be 

 merely irridescent patches as in some Alcyonarians, or they 

 may be much differentiated as in the fishes, where they consist 

 generally of rows of luminous spots, and reach their summit 

 of development in Ipnops, where they form two lantern-like 



