150 NATURAL SCIENCE [September 
very small. These results are due, on the one hand, to the luxuriant 
growth of corals, and on the other hand, to the actual scarcity of the 
bottom flat-fish or pleuronectids, which with the allied gadoids form 
the most important elements of our northern fisheries. 
The scientific results are of some value. It is to be noted that 
in many cases in which the lead indicated a sandy bottom, the trawl 
showed the presence of dense masses of coral, a fact which should be 
noted by coral-reef theorists. Mr J. E. Duerden, of the Jamaica 
Museum, gives an able summary of the fauna. Sergia, an actino-zoan 
commensal with a sponge, was re-discovered, and sponges and alcyon- 
arians were found in great abundance. ‘The edible fishes were not 
abundant, either in actual quantity or in number of species. Jesoprion, 
Ocyurus, Haemulon, and Serranus appear to be the most important. » 
Apparently the local supply in Jamaican waters will in future, 
as heretofore, have to depend upon the use of lines and drift-nets. 
ASCIDIANS AND BIPOLARITY 
We have more than once directed attention to striking cases of 
distribution, indicating some connection between the North Pacific 
and North Atlantic. Now comes Professor Herdman (77rans. Liver- 
pool Biol. Soc., xii., pp. 248-267, pls. xi.-xiv., June 1898) and draws 
up lists of closely-allied species of ascidians from Puget Sound and 
our own N, Atlantic coasts; similar series are, he says, shown in 
a subsequent paper on the Crustacea by Mr A. O. Walker. “ This, 
taken along with the similarity between the two faunas shown in 
other groups, suggests the possibility that there is a common 
northern circum-polar marine fauna which sends extensions south- 
wards on the western coasts of Europe and America.” 
Such a conception is of course opposed to the well-known hypo- 
thesis of Sir John Murray that the marine faunas towards the poles 
are genetically more closely related to each other than to any inter- 
vening fauna. Sir John has supported this ‘bipolar’ hypothesis 
by quotations from the reports of some of the specialists who 
described the “ Challenger” collections. It has struck us that this 
somewhat crude lumping of the conclusions of many minds, ex- 
pressed originally with very different ends in view, could lead to 
no secure result, and we are by no means surprised to find Mr 
Herdman commenting as follows :—*I do not know how it may be 
with other authors quoted, but in my case the series of short 
extracts given from my report require to be expanded and explained, 
and are then seen not to give Dr Murray’s view the support which 
he supposes. My remarks, on p. 265 of the Report, which he 
quotes, refer only, it may be stated, to ‘Challenger’ species. 
In the genus Styela, for example, there are plenty of species 
known from the tropics. Dr Sluiter has described about fifteen 
