G32 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 

 COUNTING OF INDIVIDUALS. 



Since the new luethod of ooeaiiic; popiiUitioii statistics introduced by 

 Hensen seeks its peculiar basis in the counting of the individuals 

 which coini)ose the plankton, and sin(;e it finds in this "counting the 

 only basis uj)on which a Judgment can rest" (9, p. 20), 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, wliicli compose the mass of the plankton, is in itself, quite a[)art 

 from its eventual value, an extremely dil'ticult 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 nmch 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, w^hich I have distinguished in the third book of 

 my " Generelle MorpJiologie,^^ 18G0, there are at least three distinct 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 {Metapliyta and Metazoa), by 



* The fonrtli part of the "Methodik'' in the i>lanktoii volume of Hensen. Avhich 

 treats of "the work on land," («) Determination of the volume, (/>) the countinjjj 

 (9, pp. 15-30), is especially worthy of readinj^, not only because it <;ives the deepest 

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

 a general biological problem, 



tThe swimming animals and plants which compose the jjlanktou should in this 

 respect be arr.'inged under the following heads: («) rrotophyta — among the Chro- 

 macew, Calcocytecv, Mnrracyicw, Xanfliellcn', Dictj/ocha', and Pey'idUiea', all single cells 

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

 aggregates. (6) Mefaphyta — ;imong t\ui Hal ouphwra are to he conutad the spherical 

 ThaUi; among the OsciUalor'uv. the singles, thread-like TliaUi ; among the Sanjasm 

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

 •are also peculiar, (c) Protozoa — the Infusoria {Nocliluca and Tintinua) as well as 

 the rhizopods {Tliiilainoiiliora and liudiolaria), are all to be counted as unicellular 

 individuals, but among the J'oh/njffariw, besides the Cccnohia (colonies of I'oUozoUhv, 

 Spkwrozoida' , and ('olIoHpha'ridai). (d) Ccclenteraia — among the Medasn- and Cteno- 

 phori'8, as also among tiie pelagic Anthozoa and Tnrhellaria 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 hero equivalent to a medusa, (c) Tanicata — among 

 the Copelata, DoJinhun, and the generations of solitary Salpas, the single persons are 

 to bo counted; on the other hand, among the Pijro.soma and the <S'a/^)rt chains, the 

 singlecormi as well as the ])ers»us which compose them, (f-l') In all the remaining 

 groM]>8 of j)lanktouic. animals, in the case of sagittii, mollusks, echinoderm larva', 

 articulates, aiul ilsluis, not nuMcOy the persons are to be counted, but also the cells 

 which mak(( up each of these metazoa. 



