448 



THE VOYAGE OF H.M.S. CHALLENGER. 



in tlie south. And since in the northern region 50 localities were explored with dredge 

 and trawl, and in the south 49 localities, the percentage proportion for the former is 

 36 per cent., as compared with 65-3 per cent, for the latter. The south tropical region 

 thus considerably exceeds the north as regards the abundance of species. 



And if in the same way we compare the two temperate zones in relation to the 

 abundance of Hexactinellid localities and species, the northern region shows, when com- 

 pared with the southern in regard to localities, 14 '4 per cent, as against 247 per cent., 

 and 26"3 per cent, as against 35'6 per cent, in regard to the number of species. 



There is thus a much greater abundance of Hexactinellids in the south temperate 

 than in the north temperate zone, which is doubtless in part referable to the much 

 greater extent of ocean in the former. 



In reo-ard further to the distribution of the subdivisions in the different zones, a 

 review of Table VI. yields the following results : — 



i 



In the north temperate zone, 

 (. In the south temperate zone. 



a. Lyssacina < In the tropics, . 



f In the north temperate zone, 

 In the tropics, . 

 In the south temperate zone, 



6. Dictyonina -j In the tropics, . 



14 species. 



26 



29 



6 



19 



6 



In relation to the total number of dredgings and trawlings the percentage proportion 

 stands as follows : — 



f In the north temperate zone, 

 a. Lyssacina -J In the tropics, 



L In the south temperate zone, 



r In the north temperate zone, 

 6. Dictyonina < In the tropics, 



L In the south temjjerate zone, 



184 per cent. 

 26-3 



28-7 „ 



7-9 „ 

 19-1 „ 



5-9 „ 



It is thus evident that throughout the Lyssacina preponderate, especially in the 

 south temperate zone, where they are almost five times as numerous as the Dictyonina, 

 while they are more than twice as abundant in the north temperate zone, and 

 preponderate by at least 7 per cent, in the tropics. 



In regard to the abundance of Lyssacina in the different zones, it is evident that 

 the north temperate zone is considerably poorer than the tropical, and that the latter is 

 excelled by the south temperate zone. 



The relation is quite different with the Dictyonina, of which the south temperate 

 zone contains the fewest, while the northern region a few more, and the tropics a relative 

 abundance. 



If the Lyssacina of the northern hemisphere be contrasted with those of the south. 



