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632 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
COUNTING OF INDIVIDUALS. 
Since the new method of oceanic population statistics introduced by — 
Hensen seeks its peculiar basis in the counting of the individuals 
which compose the plankton, and since it finds in this “counting the 
only basis upon which a judgment can rest” (9, p. 26), then we must 
examine more critically this cardinal point of his method, upon which 
he lays the greatest stress. The counting of the single organic indi- — 
viduals, which compose the mass of the plankton, is in itself, quite apart — 
from its eventual value, an extremely difficult and doubtful task. Hen- 
sen himself has not concealed a part of this great difficulty, and attempts 
to partly allay the doubts which arise against his whole method.* . But 
in fact these are much greater and more dangerous than he is inclined 
to admit. 
WHAT IS AN ORGANIC INDIVIDUAL? 
This simple question, as is known, is extremely difficult to answer, 
If one does not accept all the grades of physiological and morpho- 
logical individuality, which I have distinguished in the third book of- 
my “Generelle Morphologie,” 1866, there are at least three distinet chief 
grades to be kept apart: (1) The cell (or plastid); (2) the person (or 
bud); (3) the cormus (or colony).t Only among the Protista (Pro- 
tophyta and Protozoa) is the actual individual represented by a single 
cell; on the other hand, among the Histona (Metaphyta and Metazoa), by 
*The fourth part of the ‘‘Methodik” in the plankton volume of Hensen, which 
treats of ‘“‘the work on land,” (a) Determination of the volume, (b) the counting 
(9, pp. 15-30), is especially worthy of reading, not only because it gives the deepest 
insight into fhe error of his method, but also into his very peculiar conception of 
‘ageneral biological problem. 
tThe swimming animals and plants which compose the plankton should in this 
respect be arranged under the following heads: (a) Prolophyta—among the Chro- 
macew, Calcocytee, Murracylea, Xanthellea, Dictyocha, and Peridinee, all single cells 
are to be counted; among the diatoms partly the latter, partly the cenobia or cell 
aggregates. (b) Metaphyta—among the Halosphwra are to be counted the spherical 
Thalli; among the Oscillatorie the single, thread-like Thalli; among the Sargassa 
the cormus as well as its buds; but the cells which constitute each thallus and bud 
are also peculiar. (¢) Protozoa—the Infusoria (Noctiluca and Tintinna) as well as 
the rhizopods (Thalamophora and Radiolaria), are all to be counted as unicellular 
individuals, but among the Polycyttaria, besides the Canobia (colonies of Collozoida, 
Spherozoidw, and Collospherida). (d) Calenterata—among the Meduse and Cteno- 
phores, as also among the pelagic Anthozoa and Turbellaria the single persons are to be 
counted; among the Siphonophores these as well as the single colonies; for each person 
(or each medusom) of a cormus is here equivalent toa medusa. (e) Tunicata—among 
the Copelata, Doliolum, and the generations of solitary Salpas, the single persons are 
to be counted; on the other band, among the Pyrosoma and the Salpa chains, the 
single cormi as well as the persons which compose them. (f-k) In all the remaining 
groups of planktonie animals, in the case of sagitta, mollusks, echinoderm larvee, 
articulates, and fishes, not merely the persons are to be counted, but also the cells 
which make up each of these metazoa. 
