This paper contains a revised version of the life-history of Sacculina stressing certain points which have arisen as a result of work on the effects of the parasite on its host.

From the statistical analysis of a year’s samples of an infected crab population it is concluded; first, that crabs may be infected at any age; secondly, that the developmental sequences in the life-history of the parasite are dependent not on the season but possibly on the phases of the host; thirdly, that the internal development of the parasite lasts nine months, and that the first batches of larvae appear three months later.

Two separate experiments showed that the évagination of the parasite does not take place at an ecdysis of its host.

It is suggested that an anomalous group of highly modified male crabs without externae but containing living parasitic roots are ‘scarred crabs’ that have moulted; further, that such modified crabs will in time regenerate externae. Experimental and histological evidence supports this suggestion, but it is not held that the theory of regeneration is completely proved.

An account is given of the effects of Sacculina on the secondary sexual characters of Portunus holsatus. Only male crabs are dealt with. It is shown: (a) that various degrees of modification are possible; (i>) that the percentage of infection increases among large crabs; (c) that the smaller the crab the greater the liability to maximum modification; (d) that the maximum amount of modification which is possible decreases among larger crabs.

You do not currently have access to this content.