SCIENTIFIC SUMMARY. 
371 
ticulum of the 'wall of the polype ; and that this hud enlarges and finally 
"becomes a gonophore destined to be always attached, or a semi-medusa or 
free medusae. 
1 4. If we accept as demonstrated the facts just put forward, the gono- 
phores, the semi-medusae, and medusae cannot be regarded as sexual indi- 
viduals, and consequently it would seem that we cannot assume an alterna- 
tion of generations in these species.’ 
Geographical Distribution of the Dared Seals. — Following up the ideas put 
forward by Milne-Edwards with regard to the influence of marine currents 
upon the geographical distribution of the Penguins, M. E. L. Trouessart has 
applied the same principles to the investigation of the Eared Seals (Otariidse), 
and his results confirm those arrived at by Milne-Edwards. In the present 
epoch the Eared Seals, like the Penguins, seem to be native to the Antarctic 
lands, whence they have spread towards the north. They are conveyed 
northward on the blocks of ice which the regular currents detach and carry 
away from the great southern glaciers, and in this way have colonized all 
the southernmost coasts of both hemispheres. In the west, Humboldt’s 
current has carried them, with the Penguins, as far as the Galapagos Islands, 
situated under the Equator ; but, unlike the Penguins, the Otaries also occur 
north of the Equator, being found on the shores of California and in the 
northern part of the Pacific, but M. Trouessart concludes that the northern 
Eared Seals did not arrive at their present haunts by the direct route, seeing 
that there is a distance of more than twenty degrees between the Galapagos 
and their Californian habitat ; and further, those of the Galapagos and Cali- 
fornia belong not only to distinct species, but to different genera. 
By investigating the currents of the ocean and noting all the stations at 
which Eared Seals are met with, M. Trouessart arrives at the conclusion that 
the absence of these animals from the stretch of coast above indicated is due 
not to the higher temperature of the tropical regions, but to the action of 
contrary currents. The equatorial current of the Pacific north of the Gala- 
pagos, and that of the Atlantic north of the Falkland Islands, are directly 
opposed to the northward migration of the Eared Seals. In the Atlantic, 
those which have reached as far as Tristan d’Acunha and then attempted to 
advance in the direction of the west coast of Africa, have been carried west- 
ward by the equatorial current and driven to the coast of Patagonia. The 
Eared Seals of the Cape of Good Hope have been prevented from advancing 
along the eastern coast of Africa by the Mozambique current. Hence Eared 
Seals are absent from the Atlantic Ocean north of the Falklands, and from 
the whole western part of the Indian Ocean, having only the eastern part of 
the latter for their migration into the Northern hemisphere. 
Having reached the shores of Australia, the Otaries gradually advanced 
up the western coast, which they still inhabit, reaching in the north to Mel- 
ville Island, off Port Essington, where at least two species are found. A 
secondary current, the direction of which is determined by the Monsoon, puts 
the Indian Ocean in communication with the Chinese Sea, and from April to 
October, or exactly at the time the Eared Seals come up tow r ards the north, 
this current flows towards the north-east into the great basin of the Pacific. 
It must have facilitated the migrations of the Seals, which took place through 
the passages of the Molucca Sea, or by the broader and deeper course of the 
