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Growth-f actor.
Exceptions to this
law, as formulated
by G. H. Fowler.
The agreement between the last number and the lengtli of the mature female is of course
striking. There were, however, no larvae with shells 0,625 mm. long in this tube. In order,
if possible, to be able to complete the chain of development of this species, I went, however,
to the sample of sand etc. from whicli the specimens dealt with above had been picked out. In
this I found two complete individuals, clearly larvae in the last larval stage, and one valve
which certainly belonged to this species; these individuals had shells from 0,62—0,65 mm. in
length. The largest specimen was a male; 0,65 x 1,25 = 0,8125, i. e. about the length of the
mature male.
This example seems to show that in the case of sjoecies with a relatively constant length
of shell we may expect a far-reaching agreement even in those cases where only a small material
is present.
We must note the very slight difference in the growth-factor in different species:
Cypridina (Doloria) pectinata = 1,22, Cypridina (Vargula) norvegica = 1,21, Philomedes
globosa — 1,23, Krithe sp. - 1,245.
If thus a number of cases agree particularly well with BROOKS’s law, there are, on the
other hånd, a great many exceptions to this law to be noted. It is certain that the law is
by no means absolute. It obviously applies only with a number of restrictions and with certain
assumptions.
This has already been pointed out by G. H. Fowler himself. This investigator pointed
ont, 1909, p. 258, tliat it seemed to him possible that not only the average lengths and the
growth-factors employed by him but also ,,the law itself, as here phrased“ are approximative.
As is seen above this author has shown that the same growth-factor does not presumably apply
to ail stages in large forms with many moults (Homarus, Carcinus). He states on p. 258 that
this is presumably true „even in Ostracoda of small size and few stages“. We find this latter
assumption true in the case of the males of Cypridina (Doloria) pectinata and Cypridina
( Vargula) norvegica. On the other hand there are no such cases in G. H. FoWLER’s own examples.
Krithe sp. shows obvious variation with regard to the growth-factor. The larvae of
Conchoecia elegans can certainly be divided into well distinguished categories of length
— contrary to what G. H. Fowler observed — but they clo not permit of any simple application
of BROOKS’s law. Males and females have different growth-factors at the change from Stage II
to Stage I and at the change into the mature stage. It is to be noted that the
growth-factor is about the same for males and females at the transition from Stage II to Stage I.
I have also observed other cases that do not conform to this law, for instance Aster ope Gnmaldi,
a form that I caught in rather large numbers in the harbour at Monaco.
We must note that in the cases in which there was agreement with Brooks’s law
all the specimens that were investigated were caught at the same locality and on the
same occasion. On the other hand the water in the harbour at Monaco is subject to great
variations and the same is true, though not to such a great extent, of the water in the
Bay of Villefranche.
On pp. 227 and 228 G. II. FOWLER points out (1909) that it will probably appear
that the growth-factor is not quite identical for the same species and sex „at every
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