632 REPORT OF COMMISSIONER OF FI8H AND FISHERIES. 

 COUNTING OF INDIVIDUALS. 



Since the new method of oceanic population statistics introduced by 

 Heusen 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 i^lankton, 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 " GenereJIe Morphologic, "' 1800, there are at least three distinct chief 

 grades to be kept apart: (1) The cell (or jilastid); (2) the person (or 

 bud); (3) the cormus (or colony). t Only among the Protista {Pro- 

 tophi/ta and Protozoa) is the actual individual represented by a single 

 cell; on the other hand, among the Histouti {Mrtaphyta and 3Ietazoa), by 



* The fourth part of the "Methodik" in the plankton volnme of Hensen, which 

 treats of "the work on land," (a) Determination of the volnme, (&) the conntin<^ 

 (9, pp. 15-30), is especially worthy of reading, not only hecanse it gives the deeiiest 

 insight into the error ofliis method, but also into his very peculiar conception of 

 a general biological problem. 



tThe swimming animals and plants whicli com]>os(^ the plankton should in this 

 respect be arranged under the following heads: (r/) Protojihi/ia — among the Vhro- 

 viacecB, Calcocyletv, Mnrracyiew, XaniheUexv, TJiciiiocltw, and Peridiueo', all single cells 

 are to be counted; among the diatoms partly the latter, partly the cenobia or cell 

 aggregates, (b) MeUtpln/ia — among the /frt?os^)/(fl')Y( are to be coTiuted the spherical 

 Thalli; among the OsciUalorHV the single, thread-like ThaUi ; among tbe Sarr/assa 

 the cormus as well as its buds; but the cells which constitute each thallus and bud 

 are also peculiar, (c) Protozoa — the TnfuHorta {NoeiUuca and Tintinua) as well as 

 the rhizopods {Thalamoplwra and Padiolarta), are all to be counted as unicellular 

 individuals, but among the Pohjcuttaria:, besides the C'ocnohia (colonies of Collozoidw, 

 Sphairozoidiv, and (■ollosphwridw). (d) CoeJentcrata — among the Medusa', and Cteno- 

 phorcs, as also among the i>elagic Antkozoa and Tiirhellaria the single persons are to be 

 counted ; among the Sipho^iojihores these as well as the single colonies ; for each person 

 (or each medusom) of a cormus is here equivalent to a medusa, (e) Tunlcata — among 

 the CopeJala, Doliohon, and the generations of solitary tSalpas, the single persons are 

 to be counted; on the other hand, among the Pijrosoma and the Salpa chains, the 

 single cormi as well as the persons which compose them, (/-/i) In all the remaining 

 groups of planktonic animals, in the case of sagitta, mollusks, echiuoderm larv;e, 

 articulates, and iishes, not merely the persons are to be counted, but also the cells 

 which make up eai<-h of these metazoa. 



