TRANSACTIONS OF SECTION F). 607 



indicated, and for their solution it was suggested that oceanic expeditions should 

 be confined to the systematic study of small areas instead of making long voyages ; 

 that the upper zones of water should be investigated more minutely and with 

 more care than has hitherto been the case ; that standard tow-nets should be 

 adopted internationally by all expeditions in order to afford means of comparison 

 of the fauna in diiferent seas and under different conditions ; and that facts are 

 more worthy objects of collection than museum specimens of new species. 



3. Sterile Eggs o/ Purpura. By Professor Paul Pelseneer. 



4. Traces of a Periodic Laiv in Organic Evolution. 

 By Henky M. Bernard, M.A. 



The ' cell ' has hitherto been the only recognised unit of structure for the 

 analysis of the forms of life, and our conception of the evolutionary story has 

 never advanced beyond that of a vast multitude of cell-masses streaming through 

 time, slowly but perpetually changing their shapes, as a rule, from the simple to 

 the more complex, and in this respect diverging from one another in all directions. 

 In this stream, here and there, definite form-sequences can be recognised, but we 

 have to confess that during the last fifty years little has been done beyond 

 accumulating fragmentary evidence for the truth of the general doctrine. Hardly 

 anything of importance towards the unravelling of its underlying laws has been 

 added, and signs of weariness are betrayed in its further discussion. 



The idea embodied in this paper was arrived at from two points of view : — 



(1) Work on the stony corals suggested that the cell has not been the only 

 unit of structure. A normal coral stock, i.e., a stock not too highly specialised, 

 may be the product of at least three units : (a) the cells which, by division, build 

 up the polyp ; (A) the polyps which, by a modification of division (fission or 

 budding), produce a colony ; (c) the colonies which, by what may be a further 

 modification of division, produce a stock.^ 



This suggestion that the larger forms of life may be built up of several units 

 of structure, such as the cell and others of grades above the cell, is supported by 

 what we know, e.g., of the important place the annelids (themselves built up of 

 series of segments) hold in animal morphology, and also by the fact that in the 

 vegetable kingdom repetition of parts seems to be the almost invariable rule for 

 the building-up of the larger forms — that is, of parts which are themselves 

 complicated structures, and also possibly analysable by other {i.e., higher) 

 units than the cell. These suggestions call for a fresh survey of the whole 

 evolutionary series from this point of view — that is, in order to see whether the 

 forms of life do not reveal other units of structure above the cell ; and if above, 

 why not also below ? 



(2) The other line along which the subject was approached was a long com- 

 parative analysis of animal tissues in order to ascertain what support they give to 

 the author's description of the essential structure of the * cell layers ' of the verte- 

 brate retina." This analysis and its results, which are being put into book form, 

 have also, during the difficult process of setting them out in e.vtenso, revealed a 

 succession of structural units of increasing complexity, the cell being only one in 

 the series. 



Traces of a law of successive units of increasing complexity have thus been 

 reached along two quite distinct lines of research. In neither case was it a sudden 

 happy inspiration or mere speculation ; in both it was a conclusion slowly forced 



' This point is worked out in further detail in vol. vi. of the British Musemn 

 Madreporaria, now in the press. 



' See Retinal Studies, Part VI., Quarterli/ Journal of Microscopic Science, vol. 47 

 pp. 303-362, pis. 27-29. 



