336 
POPULAK SCIENCE EEVIEW. 
therefore a true pigmentary colour. The only explanation he can offer to 
account for this peculiar appearance of colour is this: — It is well known 
that during the breeding season fishes frequently take on the most brilliant 
colours, which disappear when that season is past. It is not therefore im- 
probable that this colour may have been one, at least, of the colours assumed 
by the fish during the reproductive period, and that the alcohol served in 
some way to bring out the colour thus abnormally. Whatever may have 
been the cause, the fact that colour can so appear in fishes will serve as a 
caution to ichthyologists when describing species from alcoholic specimens 
alone, lest they confound abnormal or seasonal colours with those that are 
permanent. 
Parthenogenesis among Lepidoptera . — It seems that the* Dutch naturalist, 
M. H. Weizenbergh, jun., has performed a series of experiments on this 
interesting subject, the insect placed under observation being Liparis dispar, 
and concludes that it is possible for at least three successive generations to 
be produced without access of the male to the female. The following are 
the results of his very careful experiments : — (1) August 18(36, eggs laid 
by impregnated females; April 1867, caterpillars appear, and in July per- 
fect butterflies. (2) August 1867, eggs laid by females of this year are 
without impregnation ; April 1868, caterpillars appear, and in July perfect 
butterflies. (3) August 1868, eggs laid by females of this year without 
impregnation ; April 1869, caterpillars appear, and in July perfect butter- 
flies. (4) August 1869, eggs laid by the females of this year without im- 
pregnation; April 1870, no results, , the eggs all dried up. The power of 
reproduction appeared to decrease year by year when impregnation was 
prevented. Similar results have been noticed in other butterflies, in bees, 
and notably in aphides. 
An Error of Mr. Dancin' s . — The 11 American Naturalist” (May 1872) 
states, that in the last edition of his u Origin of Species,” Mr. Darwin mis- 
states Hyatt and Cope’s law of acceleration and retardation in the following 
language : u There is another possible mode of transition, namely, through 
the acceleration and retardation of the period of reproduction. This view 
has lately been insisted on by Prof. Cope and others in the United States. 
It is now known that some animals are capable of reproduction at a very 
early age, before they have acquired their perfect characters,” &c. A 
writer, who signs himself “Z,” states, that Prof. Cope and others have not 
insisted on the above propositions, which he imagines to be supported by 
very few facts. Their theory of acceleration and retardation states, that, 
while the period of reproductive maturity arrives at nearly the same age or 
period of the year in most individuals of a single sex and species, the por- 
tion of the developmental scale which they traverse, in that time may vary 
much. That an addition to the series of changes traversed by the parent 
would require, in another generation, a more rapid growth in respect to the 
series in question, which is acceleration. A falling short of accomplishing 
that completeness would result from a slower growth, hence the process is 
termed retardation. Vast numbers of observed facts prove that this is the 
great law of variation, towards which little progress has yet been made by 
students who are yet chiefly occupied with the co-operative law of natural 
selection. 
