604 REPORT OF COMMISSIOXER OF FI.SII AND FISHERIES. 



Botli of tlie i;eiun'a bcloiii^iii.n' tlnu'e {7£al(>h((f(;s and llalolxdadcs, witli 

 about Ji do/eu species) are limited to the tropical luid subtropical zone. 

 The ChaUoujer found theni in the Atlantic between 35'^ uorth latitude 

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

 23° south latitude. 1 myself observed HnJohaies numerously in the 

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

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



J. — TuxiCATKs OK Tin: Plankton". 



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

 to their mode of life. The ascldlans belong to the benthos; all other 

 tunieaten to the plankton. Tlie Copelata (or Appendicular idw) are mor- 

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

 the nearest of the now living relatives of the Prochordinuv, the hypo- 

 thetical common ancestor of the tunicates and vertebrates (30, p. 00")). 

 The near relationship of the Gopelata and the ascidian larva makes it 

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

 primarily pelagic (Jopelata, aud has diverged from this through the 

 acquirement of a sessile mode of life. The Lncidke or Pyrosomida', on 

 the other hand, are probably secondarily pelagic aninmls, aud sprang 

 from the (Jwlocorniida', a benthonic synascidiau group. The Thalidiw 

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

 pelagic animals. These conditions are doubly interesting, because the 

 tunicates in an exemplary manner demonstrate the peculiarities which 

 the transition on one side to a sessile mode of life in 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 tunicates), has brought 

 about. All the latter are transparent and luminous fragile auimals, 

 poor in genera and species, but 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 

 and species, in many ways adapted to the manifold local coiulitions of 

 the bottom, and mostly opaque. The few hyaline forms {e. //., Cla rellina) 

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

 diverged from the pelagic Copelata. 



All i)lanktonic tunicates are exquisite oceanic animals aud all maj^ 

 a])])ear in immense swarms of astonishing extent. Murray (0, ]>]). 170, 

 521, 738, etc.) and Chierchia (8, pp. 32, 53, 75, et<;.) nn^t with great 

 swarms of Append! cnlaria, Pyrosoma, Doliolum, and ^Salpa in the middle 

 of the open ocean, both in the Atlantic and Pacific, parti<'u]arly in the 

 ('(piatorial zoue. 1 observed the same in the Indian Ocean, between 

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

 T//r//<V/<Vr, which Captain llabbe (•(►llected 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 Salpa aud Pyro- 

 soma on theo])en sea, far from all coasts, .are spoken of. On the other 



