1912] Ritter: The Marine Biological Station of San Dic go 201 
is to be hoped that this investigation may be followed up in the 
not distant future. 
In the study of enteropneust larvae by Ritter and Davis, 
already noticed, three quite distinct stages in the larval develop- 
ment were recognized and correlated with different habit-of-life 
periods of the larva. This class of studies, that of tracing in 
detail the relation between structural features in pelagic larvae 
and modes of life in nature at different periods, has yielded 
instructive results wherever pursued and so promises well for 
future work. 
The four papers, Ritter and Bailey (1908), Ritter (1909b), 
Johnson (1910), and Ritter and Johnson (1911), are concerned 
with a common developmental problem notwithstanding the wide 
diversity in title and special topics. The problem may be stated 
thus: To what extent do the members of the repetitive growth 
series so obvious and widely prevalent in organie beings fall into 
groups of such sort that each member is a function, in the 
mathematical sense, of the position it occupies in the series to 
which it belongs? Stated in another way the problem is: How far 
are the periodic phenomena so common in organisms expressible 
in terms of systematic quantitative difference for different parts 
of the observed periods? It will be noticed that the problem 
involves not only one of fact as regards organic phenomena, but 
also for its solution, one of method, that of systematic quantita- 
tive determination within the confines of individual organisms. 
The second paper mentioned (Ritter, 1909b) contains an 
account of the initial attack upon the problem. The results, so 
far as they pertain to this problem, are summarized in the fol- 
lowing quotations: ‘‘An approximately exhaustive study of one 
of the animals finds it to contain a manifolding of similar parts 
to an extent that is surprising in view of the slight prevalence 
of such parts recognized by cursory observation. Comparison of 
many individuals of various sizes and ages... . reveals the 
fact that to a large extent, the measure of which is not known, 
these manifolded parts have arisen (a) as lineally genetic series 
.... from a few initial ancestral organs; while others have 
arisen (b) as repeated productions from common original sub- 
strata, or menstrua. Attention to these repetitive series makes 
