N. Annandat^e : The Indian Cirripedia Pedunculata. 
67 
1909.] 
is artificial. The question need not arise as regards genera containing a small number 
of species, for in such cases it is clear that the multiplication of divisions is unnecessary 
and apt to confuse rather than elucidate. In the case of species, however, I am in 
favour of only recognizing those which are clearly different from one another and 
separated by a distinct gap in the line of variation. Narrow gaps as regards structure, 
which cannot be bridged over completely, exist between the offspring of a single parent 
or pair of parents, as we see in the larger animals, in which they are easily detected; 
and narrow gaps, a little wider in many cases, are clearly visible between the children 
of different parents. It is impossible to take notice of all such gaps, many of them 
being incapable of detection by the senses and rather inferred than proved to exist, 
while others, which can be detected, are so inconstant, and obey any known law so 
little, that to recognize them causes confusion and does not assist in a rational 
system of classification. There are other narrow gaps which can not only be detected 
but also proved to separate large groups of individuals to some slight extent. They 
are still so narrow, however, that they can only be detected by the closest study 
(or even by a comparison of specimens), and are not sufficiently marked to be used as 
arguments in proving any divergence in genetic relationship between the groups they 
separate. 
Groups thus separated are peculiarly common in the Cirripedes and occur in many 
species of Lepadidæ. To regard them as distinct species would militate against any 
investigation of the geographical distribution of the group , and would only complicate 
its study from a morphological point of view. It must be clearly understood, more- 
over, that the gap which separates them is not of the same nature in all cases, or due 
to the same causes ; and therefore it is inadvisable to call all of them either ' ‘ varie- 
ties,” “ .subspecies,” or races,” or to designate them in any other way that fails 
to mark their divergence in character. 
Apart from developmental phases, which have been little studied in the Tepadidæ 
and are not always easy to distinguish, we find that the smaller groups into which 
the species may be divided are mainly of two kinds. In the first place it is easy to 
prove that certain species are peculiarly liable to give rise to local races, the indivi- 
duals of which are more or less constant among themselves and differ from individuals 
from any other locality. Such groups I have called races or subspecies. Another 
kind of group, however, occurs not infrequently, consisting of a number of individuals 
not separated by any geographical boundary from others of the same species but 
differing from the typical form {i.e., the form first described) in unimportant charac- 
ters, which may or may not be hereditary. Such groups I have called “ varieties.” 
In most cases there is nothing definite to prove whether the varieties of a species 
do or do not interbreed, but the probabilities are in favour of the former mode of 
propagation. 
The best example of a species with different races that I know among the 
Lepadidæ is Pœcilasma kœmpferi, which occurs in its typical form in Japan and theS. 
Pacific but is represented by subspecies in several different parts of the Indian and 
Atlantic Oceans. True varieties are less common among the Tepadidæ than they are 
