44 
Parasitism 
characters by the female. Later research however does not support 
his conclusion. 
In addition to describing the remarkable series of changes in the 
secondary sexual characters, Giard elucidated a second cardinal point, 
namely that the influence of the parasite on the genital glands of the 
hosts is such as to cause dwindling and subsequently entire disappear¬ 
ance. This induced sterility, in some Crustacea the invariable ac¬ 
companiment of these associations with Sacculina, accounts for the 
name bestowed on this phenomena by its discoverer—“ la castration 
parasitaire.” 
A long series of observations form the continuation of this early 
work and it is sufficient to say that the occurrence of changes as the 
result of parasitic infection have been demonstrated in most animal 
phyla either directly by Giard or others inspired by his researches. 
The cases of sterility accounted for by internal parasitism are now very 
numerous; but in few of these are the secondary sexual characters so 
well defined as to exhibit the corresponding changes in the external 
characters. The instances which most fully exhibit the nature of the 
phenomenon are all found in the Arthropoda where the possession of 
a chitinous exoskeleton allows of the expression of very definite sexual 
differences. 
One case may well be quoted here. The singular modifications 
to which bees of the genus Andrena are subject, are traceable in every 
case to the fact that they harbour the larvae of the extraordinary 
insect Stylops. The phenomena of “ stylopisation ” have always been 
familiar to entomologists and have rendered the systematic study of 
these Hymenoptera exceedingly difficult. So distinctive are the changes 
which this insect parasite produces, that many species have been 
erroneously grounded on parasitised forms. 
It must be pointed out that alterations of the reproductive system 
are nearly always due to parasites which exist in the body cavity and 
blood spaces of tbe host. This class might well be expected to exert 
a more powerful influence on the general metabolism of an infected 
organism than the intestinal parasites. Save for two exceptional cases 
described at the end of this paper we know of no cases of connection 
between the existence of large numbers of parasites in the gut and 
anomalies in the sexual organs. Before leaving the discussion of the 
scope of the phenomenon it may, too, be pointed out that no such 
effects have yet been observed in vertebrate animals. The extension 
of helminthological studies has resulted, for example, in the discovery 
