46 THE VOYAGE OF H.M.S. CHALLENGER. 



■men*, the multiplication of similar parts rather than differentiation into dissimilar, — 

 that the onus 2>i'ohandi obviously lies on those who would find in them a vera causa for 

 that advance of development, which shows itself in the j^^'odiiction of the forms among 

 which " natural selection " is to operate. A single di-edging brings up three types of 

 Orbitolites, all living and thriving on the same bottom, and therefore, it may be inferred, 

 equally well adapted to their common " environment "; yet one is of the very simplest 

 structure and limited size, whilst another is of extraordinarily complex structure, and of 

 comparatively gigantic dimensions. And it is difficult to imagine that the " complex " 

 structure of the large shelly disk of Orbitolites complanata can give it the least advantage 

 in the " struggle for existence " over the small and " simple " Orbitolites marginalis 

 which is livinor along side of it. 



Again, while abundance of food and a favourable temperature might produce in the 

 spiral shell of Cornaspira a large extension upon the same simple plan, we can scarcely 

 attribute to any such influences the peculiar change that shows itself in the periodical 

 interruption of growth by the formation of a partial septum, which converts it into a 

 Spiroloculina. Still less would it give any account of the formation of the complete 

 septum traversed by a row of pores, which marks the assumption of the Peneroplis type ; 

 or of the subdivision of the spu'ally-growing chambers into chamberlets, which lifts it 

 upwards into an Orbicidina ; or of the exchange of the spiral for the cyclical plan of 

 growth, which converts it into an Orbitolite. For what possible advantage can be 

 supposed to be gained by any of these modifications, when we find that all those 

 intermediate types, which show them in various grades of advance, — as if arrested in 

 their developmental progress, — maintain their ground under exactly the same conditions, 

 as though none had passed them in the race ? 



Looking now to the other essential condition of the " environment " of 

 Orbitolites, — the preying of higher marine animals upon them,— I find it difficult to 

 conceive that any of the foregoing modifications of structure can give to either type the 

 least advantasje in the " strugQ-le for existence." We know that the smaller Foraminifeea 

 serve as food both to Echinoidea and to Asteroidea, since the stomachs of these animals are 

 found to be full of them ; and it is probable that the larger forms are eaten by Crustacea 

 and Fishes. But it seems scarcely possible that such creatures can have any preference for 

 a cyclical over a spiral form, or for a complex over a simple. The very fact that — like 

 the vast variety of Oj^ercidince which I formerly described (Phil. Trans., 1859, p. If)) 

 from Mr. Cuming's gatherings — they all abound in the same localities, seems to forbid 

 the idea that any one form is better fitted for survival than another. Getting out of the 

 way of enemies is obviously out of the question with Fokaminifeka ; and the Fishes 

 whose teeth are adapted to browse upon hard Corals, wovdd not be likely to pick out one 

 species of Orbitolite from another, when even a practised Foraminiferalist cannot 

 distinguish them without examination with a ma^nifvins-glass. 



