Stiiflies on marine Ostracods 



147 



geographical position and sea-climate". It remains as a fact that the same species has different 

 sizes at different localities. Thus the specimens of Philomedes globosa measured by me were 

 only 2,4 — 2,6 mm. at Skager Rack while the same species attained a length of 2,9 — 3,1 mm. 

 at Greenland. This difference in length is not due to the species undergoing a different 

 number of moults before maturity under different external conditions. The number of larval 

 moults in the Cypridinid group seems to be constant for every species, as is shown above. 

 Corresponding classes of length were found at the different localities, but the absolute measure- 

 ments are different; cf. Philomedes globosa. This difference in length really seems often to 

 be accompanied by a difference in the growth-factor. Unfortunately my material was not 

 large enough to work out a definite answer to this problem by means of it. A fact that 

 supports, however, the idea that there is sometimes an alteration of the growth-factor is that 

 the embryos in the brood-chamber of large individuals are often not essentially larger than 

 those in small individuals. (In the large individuals, on the other hand, the number of embryos 

 is often larger than in small individuals.) 



The final result of my investigations is thus that the 

 g r o w t h - f a c t o r d vi r i n g the p o s t - e m b r y o ii a 1 development of the 



s t r a c o d s is presumably an i n li e r i t c d factor, but it is rather 

 strongly influenced by external circumstances; in addition in 

 a number of species it is not quite the sa m e during the wiiole 

 p o s t - e m b r y o n a 1 d e v e 1 o ji m e n t. It thus seems as if Brooks's law, as formulated 

 by G. H. Fowler, 1909, p. 224, needs a not inconsiderable modification. Before it is 

 re-formulated, however, it will be necessary to investigate a still larger material; moreover the 

 importance the abimdance of nourishment, temperature and other external conditions for the 

 rapidity of growth must first be studied. 



In spite of this the law even as formulated at present seems to be very useful. G. H. 

 Fowler himself has estimated it correctly when he says, 1909, p. 258: „0n the other hand, 



1 have little doubt that the law as phrased on p. 224 is a sufficiently accurate weapon for the 

 zoologist to use in combination with the morphological evidence, even if the words ,,f i x e d 

 percentage" may require revision at the hands of the ruathematician". 



Summary of the 

 res alls of my in- 

 vestigation of this 

 problem. 



