332 University of California Publications in Zoology \Vou.9 
The general trend of the data concerning the distribution of the 
Copepoda is in line with the discussion in the papers of Kofoid 
(1907a, 1907b). He shows for a number of plankton animals 
that in general the species which are more closely related strue- 
turally have a coincident instead of a contiguous distribution. 
This might also be inferred as true of the pelagic Copepoda, 
since so many of them are found at the same depths during the 
day. As particular examples may be mentioned Gaetanus wni- 
corms and G. secundus, which, structurally, form a very closely 
related pair of species; secundus was taken in but one haul with 
the Kofoid net, but then it was in company with a specimen of 
unicornis.  Huchirella galeata and E. pulchra form a couplet: 
the former was taken in but three hauls with the Kofoid net, 
always with pulchra. Scolecithrix magna appeared in but three 
hauls of this character, two of which contained S. frontalis, a 
rather closely related species. The four species of Plewromamma 
found in this region occurred together repeatedly in the closing 
nets and P. abdominalis and gracilis were taken together in the 
seven hauls that contained gracilis. It is hard to say how much 
these examples mean until we know more about breeding ranges 
and seasons as well as the general hydrographic conditions in 
deep water, where all of the species mentioned are found in 
greatest abundance during the day. 
It is important to note again, however, that, even with our 
lack of knowledge concerning the conditions under which the 
Copepoda live, the forms we know most about show differential 
characters in other respects than structure. The species grouped 
”? 
in the ‘‘couplets’’ mentioned above are so placed because of 
morphological characters. If our knowledge of them in other 
matters were as extensive we might find that they are examples 
of species that are quite different from each other but with a 
similar distribution. That is, if the behavior, for example, of one 
species of Gaetanus should prove to be markedly unlike that of 
the other, there would be justification for the view that these are 
distantly related forms; and even if they should always be taken 
in the same hauls with the Kofoid net, it would at least be a 
matter for argument if they were not examples of the coincident 
distribution of distantly related species. That would depend on 
