102 CRUSTACEA CHAP. 
copulatory styles typical of the male, but also the four pairs of 
ovigerous appendages typical of the female. The parasitised 
females, on the other hand, though they may show a degenerate 
condition of the ovigerous appendages (Fig. 72, D), never develop 
a single positively male characteristic. On dissecting crabs of 
these various categories it is found that the generative organs 
are in varying conditions of degeneration and disintegration. 
The most remarkable fact in this history is the subsequent 
behaviour of males which have assumed perfect female external 
characters, if the Sacculina drops off and the crabs recover from 
the disease. It is found that under these circumstances these 
males may regenerate from the remains of their gonads a perfect 
hermaphrodite gland, capable of producing mature ova and 
spermatozoa. The females appear quite incapable, on the other 
hand, of producing the male primary elements of sex on recovery, 
any more than they can produce the secondary. Exactly 
analogous facts have been observed in the case of the hermit- 
crabs parasitised by Peltogaster, but here the affected males 
produce small ova in their testes before the parasite is got rid 
of. Here, too, the females seem incapable of assuming male 
characters under the influence of the parasite. 
To summarise shortly the conclusions to be deduced from 
these facts—certain animals react to the presence of parasites 
by altering their sexual condition. This alteration consists in 
the female sex in an arrest of reproductive activity, in the male 
sex in the arrest of reproductive activity coupled with the 
assumption of all the external characters proper to the female. 
sut in these males it is not merely the external characters that 
have been altered; their capacity for subsequently developing 
hermaphrodite glands shows that their whole organisation has 
been converted towards the female state. That this alteration 
consists in a reorganisation of the metabolic activities of the 
body is clearly suggested, and in the succeeding paragraph we 
furnish some further evidence in support of this view. 
Partial and Temporary Hermaphroditism. High and 
Low Dimorphism. 
The reproductive phases of animals are frequently rhythmic, 
periods of growth alternating with periods of reproduction. 
