170 THE RATE OF GROWTH [ch- 



larva. At the root of the matter hes the simple fact that meta- 

 morphosis involves wastage of tissue, increase of oxidation, expendi- 

 ture of energy and the doing of work. While as a general rule the 

 better the animals be fed the quicker they grow and the sooner they 

 metamorphose, Barfurth has pointed out the curious fact that a 

 short spell of starvation, just before metamorphosis is due, appears 

 to hasten the change. 



The negative growth, or actual loss of bulk and weight which 

 often, and perhaps always, accompanies metamorphosis, is well 

 shewn in the case of the eel *. The contrast of size is great between 

 the flattened, lancet-shaped Leptocephalus larva and the httle black, 

 cylindrical, almost thread-Uke elver, whose magnitude is less than 

 that of the Leptocephalus in every dimension, even at first in length 

 (Fig. 38), as Grassi was the first to shew. 



The lamprey's case is hardly less remarkable. The larval or 

 Ammocoete stage lasts for three years or more, and metamorphosis, 

 though preceded by a spurt of growth, is followed by an actual 

 decrease in size. The little brook lamprey neither feeds nor grows 

 after metamorphosis, but spawns a few months later and then dies; 

 but the big sea-lampreys become semi-parasitic on other fishes, and 

 live and grow to an unknown agef. 



Such fluctuations as these are part and parcel of the general flux 

 of physiological activity, and suggest a finite stock of energy to be 

 spent, now more now less, on growth and other modes of expenditure. 

 The larger fluctuations are special interruptions in a process which 

 is never continuous, but is perpetually varied by rhythms of various 

 kinds and orders. Hofmeister shewed long ago, for instance, that 

 Spirogyra grows by fits and starts, in periods of activity and rest 

 alternating with one another at intervals of so many minutes { 

 (Fig. 39). And Bose tells us that plant-growth proceeds by tiny and 

 perfectly rhythmical pulsations, at intervals of a few seconds of time. 



* Johannes Schmidt, Contributions to the life-history of the eel, Rapports 

 du Conseil Intern, pour V exploration de la mer,y, pp. 137-274, Copenhagen, 1906; 

 and other papers. 



t Cf. {int. al.) A. Meek, The lampreys of the Tyne, Rep. Dove Marine Laboratory 

 (N.S.), VI, p. 49, 1917; cf. L. Hubbs, in Papers of the Michigan Academy, iv, 

 p. 587, 1924. 



% Die Lehre der Pflanzenzelle, 1867. Cf. W. J. Koningsberger, Tropismus und 

 Wachstum (Thesis), Utrecht, 1922. 



