168 Frojessor H. N. Moseley [Jan. 23, 



WEEKLY EVENING MEETING, 



Friday, January 23, 1885. 



8iB Febdeeiok Beamwell, F.R.S. Manager and Vice-President, 

 in the Chair. 



Peofessor H. N. Moseley, M.A. F.E.S. 



The Fauna of the Seashore. 



The marine fauna of the globe may be divided into the littoral, the 

 deep-sea, and the pelagic faunas. Of the three regions inhabited by 

 these faunas, the littoral is the one in which the conditions are most 

 favourable for the development of new forms through the working of 

 the principle of natural selection. As Professor Loven writes, " The 

 littoral region comprises the favoured zones of the sea where light 

 and shade, a genial temperature, currents changeable in power and 

 direction, a rich vegetation spread over extensive areas, abundance of 

 food, of prey to allure, of enemies to withstand or evade, represent an 

 infinitude of agents competent to call into ]}laj the tendencies to vary 

 which are embodied in each species, and always ready by modifying 

 its parts to respond to the influences of external conditions." It is 

 consequently in this littoral zone, where the water is more than 

 elsewhere favourable for respiration, and where constant variation of 

 conditions is produced by the tides, that all the main groups of the 

 animal kingdom first came into existence ; and here also, probably, 

 where the first attached and branching plants were developed, thus 

 establishing a supply of food for the colonisation of the region by 

 animals. 



The animals inhabiting the littoral zone are most variously modi- 

 fied, to enable them to withstand the peculiar physical conditions 

 which they encounter there. Hence the origin of all hard shells 

 and skeletons of marine invertebrata, various adaptations for boring 

 in sand, the adoption of the stationary fixed condition, and similar 

 arrangements. Almost all the shore forms of animals, however 

 inert in the adult condition, pass through in embryological develop- 

 ment free-swimming larval stages which are closely alike in form for 

 very widely difierent groups of animals. Thus the oyster and most other 

 mollusca of all varieties and shapes when adult, develop from a free- 

 swimming pelagic trochosphere larva, and so do many annelids. Such 

 larvae cannot be of subsequent origin to the adults of which they are 

 phases. If such were the case, they would not have become so closely 

 alike in structure. In reality they represent the common ancestors 

 from which all the forms in which they occur were derived, and as 

 all these larvjo are pelagic in habits and structure, it follows that the 



