604 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



Botli of the genera beloDging tliei-e {Ilalohates and Htdohdtodcs, witli 

 about a clozea species) are limited to the tropical aud subtropical zoue. 

 The Challenger fouud them iu the Atlantic between 35'^ north latitude 

 aud 20^ south latitvule; iu the Pacific between 37'^ north latitude aud 

 23° south latitude. I myself observed Halobates numerously in the 

 Indian Ocean, and on one day iu crowds in the neighborhood of Belli- 

 gam. Although they can dive, they never go into the depths. 



J. TUXICATKS OF THK PLAXKTOX. 



The tribe of mantle animals falls into two chief divisions, according 

 to their mode of life. The ascidlans belong to the heuthos; all other 

 tunieates to the plankton. Tlie (Jopelata (or Appendicular l(la')'dve mor- 

 phologically the oldest branch of the stem, and are to be regarded as 

 the nearest of the now living relatives of the FrocJiordiniw, the hyr»o- 

 thetical common ancestor of the tunieates and vertebrates (30, p. ()0."i). 

 The near relationshi]) of the Gopelata and the ascidiau larva makes it 

 very probable that the whole class of ascidians has sprung from the 

 primarily i>elagic (Jopelata^ and has diverged from this through the 

 acquirement of a sessile mode of life. The Liicidue or Pyrosomidce, on 

 the other hand, are probably secondarily j)elagic animals, and sprang 

 from the (Jwlocorniida', a benthouic synascidiau g'roup. The Thalidke 

 (the DolioUdic as well as the Salpid(v) are to be regarded as primarily 

 pelagic animals. These conditions are doubly interesting, because the 

 tunieates in an exemplary manner demonstrate the peculiarities which 

 the transition on one side to a sessile mode of life iu the benthos (in 

 case of the ascidians), and on the other to a free-swimming mode of 

 life in the plankton (in the case of all other tunieates), has bronght 

 about. All the latter are trans[)arent and luminous fragile animals, 

 poor iu genera and species, bat rich in numbers of individuals. The 

 ascidians, on the other hand, fastened to the bottom, in part littoral on 

 the coast, in part abyssal in the deep sea, are much richer in genera 

 aud si^ecies, iu many ways adapted to the nmnifold local conditions of 

 the bottom, and mostly opaque. The few hyaline forms {e. <j., ClavelUna) 

 may be regarded as the remnant of the old ascidian branch, which 

 diverged from the pelagic Copelata. 



All planktonic tunieates are exquisite oceanic animals and all may 

 appear in immense swarms of astonishing extent. Murray (G, ])p. 170, 

 521, 738, etc.) and Chierchia (S, pp. 32, 53, 75, etc.) met with great 

 swarms of Appendicularia, Pyrosoma, Doliolum, and Salpa in the middle 

 of the open ocean, both iu the Atlautic and Pacific, i^articularly in the 

 equatorial zone. I observed the same in the Indian Ocean, between 

 Ceylim and Aden. Further, I have whole bottles full of closely i)ressed 

 Thalidia',^y\u(i\l Captain lialibe collected in the middle of the Atlantic, 

 Pacific, and Indian oceans, far removed from all coasts. In many log 

 books also these swimming and luminous crowds of iSalpa and Fyro- 

 soma on the open sea, far from all coasts, are spoken of. On the other 



