AND ITS EFFECT ON THE CRAB AND LOBSTER FISHERIES. 263 



less than three, and may mount up to seven or eight in certain species 

 {e.g. M. radix, Fischer's Conchy liologie, p. 641, fig. 399). The value, 

 from this point of view, which should be given to the ridges on the 

 shells of ammonites (extinct cuttlefishes) is doubtful. Woodward (loc. 

 cit.) suggests that they may indicate the age of the shell in years 

 (20 to 100); but there is no more ground for this conclusion than 

 there would be for the opinion that the septa in the shell of a Nautilus 

 or a Spirilla were of annual formation. Both structures are intimately 

 connected with the growth and support of the body, but their formation 

 cannot be dependent on any annual periodicity of growth, since Spirula 

 at any rate lives in the abysses of the ocean (350 to 950 fms.) far 

 below the influence of seasonal changes. On the other hand it is not 

 impossible that the larger and thicker varices which occur at intervals 

 along the shells of certain ammonites may indicate the extent of one 

 year's growth (Fischer and Woodward, loc. cit., pi. iii., figs. 9 and 12). 

 On this basis the age of the specimens figured could be estimated at 

 five or six years. 



From the facts recorded above concerning the rate of growth of 

 oysters and the larger gastropods, it seems clear that the larger 

 mollusks require at least three or four years to attain their full normal 

 size. The octopus which have infested our coasts this year have been 

 of various dimensions, but great numbers of them have been of 

 phenomenal size, the arms in many cases attaining a length of 3 feet, 

 and in some a length of 3J feet from the mouth to the tip of the 

 arm. 



As specimens exceeding these in size are of very rare occurrence, 

 we may assume provisionally that the age of the oldest specimens is 

 at least three or four years, and, upon Woodward's theory of cephalopod 

 growth, may far exceed that limit. The case of Spirula seems to me 

 to be alone sufficient to discredit the accuracy of Woodward's theory ; 

 and a maximum age of seven or eight years for the largest specimens of 

 octopus caught this year is the utmost that I should be prepared to 

 assign from the analogy of other mollusks. 



These estimates are probably sufficiently accurate to support the view 

 that the plague of octopus may be traced to the influence on the repro- 

 duction of this species of the exceptionally favourable conditions which 

 prevailed in 1893. If reference be made to the third volume of this 

 Journal (pp. 210, 211) it will be seen that the conditions which prevailed 

 in that year on our southern shores, as well as on the coasts of France, 

 were extraordinarily favourable* for the reproduction of marine animals, 

 and resulted in a great increase of the smaller mollusks, hydroids, and 



* The spring quarter was the warmest recorded in our islands for at least thirty-three 

 years, and was succeeded Ly a liot, calm summer (see this Journal, vi. p. 68, Table G). 



NEW SERIES. — VOL. VI. NO. 2. T 



