608 TRANSACTIONS OF SECTION D. 



on the mind after years of working at the facts. During the second line of work 

 the possibility was further perceived (1) of defining what constituted a unit of 

 organic structure ; (3) of showing that the progress from unit to unit could be 

 described in a formula, this being in each case essentially the same, and differing 

 oply in the increased complexity of the factors. 



Given, then, (1) the discovery of four or five units of animal structure, all alike 

 in so far as they show certain definite characteristics which make them capable 

 of acting as units of structure ; and (2) the fact that the morphological transfor- 

 mations by which the units are successively evolved out of those wliich go before 

 follow essentially the same course in each case, the inevitable conclusion is that 

 & periodic laiv underlies the evolution of organic life. 



So far the author believes that five consecutive units in the animal series, with 

 a considerable number of the connecting links, are distinctly recognisable among 

 existing forms, and, further, that it will be found to follow, as a natural inference 

 from these five ^natural because the processes can be formulated — and there is no 

 reason to believe that a formula which is true for the five should be suddenly 

 broken) that at lea.st one lower and one higher unit can be sketched in outline. 



Quite apart from the theoretical interest attached to the fact of periodicity and 

 all that it now means, and may in the future mean, comes the interest in the 

 actual details, such as, for instance, the possibility afforded of assigning to groups 

 of both animal and vegetable organisms, which have hitherto been difficult to 

 account for, places of origin from this or that ' period.' 



Lastly, the author, being a zoologist, has naturally confined himself to the 

 animal series ; but the animal and vegetable series are found to meet at a point 

 which it seems now possible more clearly to define, and one of the objects of read- 

 ing this paper now, rather than waiting a year or so till the book is published, is 

 to appeal to the botanists for their evidence for or against what appears to be a new 

 evolutionary law. 



5. On the Relation of Scientific Marine Investigations to Practical 

 Fishery Problems. By Dr. E. J. Allen. 



6. The International Investigation of the North Sea Fisheries. 

 By Dr. W. Garstang. 



WEDNESDAY, AUGUSTS. 

 The following Papers were read : — 



1. Notes on the Habits of Galatheidje. 

 By Miss E. F. Galloway and Herbert J. Fleure. 



The numerous moults and the tough coats of most of the Decapod Crustacea 

 are disadvantages for animals of swimming habit, and in many members of this 

 group the habit is a waning one. The shore forms of Gnlatheidce may be described 

 as descendants from swimming ancestors adapted to a life clinging to the undersides 

 of boulders. 



Galathea squamifera may progress by flapping the permanently bent abdomen, it 

 may lurk in holes with chelipeds outstretched for prey, it may walk in almost 

 crab-like fashion, or it may, and most often does, cling to the lower surface of a 

 large boulder. "When clinging, the walking legs are spread out as radial grap piers, 

 the centre of the ellipse being the longitudinally concentrated ventral thoracic 

 ganglia. The walking legs have lost their chelae, and to a great extent their 

 cleaning function, and end in grappling-hooks; but the last thoracic limb, though 



