268 THE BIOLOGY OF THE SEA-SHORE 



Cirripedes. — Ks hinted already, both the sedentary rock 

 barnacles and the parasitic Sacculina are hermaphrodite 

 species. The young barnacle is hatched as a Nauplius, 

 passes after a short period into a Cypris stage and eventually 

 fixes itself head downwards by means of a cementing 

 substance secreted by the first antennae. According to 

 Orton {op. cit.), Balanus halanoides attains to full size in a 

 year and gives off large numbers of nauplii at this age, 

 but there does not seem to be more than one breeding 

 season, namely, in the late winter months. 



Sacculina, the adult of which is little more than a bag of 

 gonads, is also hatched as a typical Nauplius except for the 

 absence of an alimentary canal. It passes into a Cypris 

 stage, the larva after a period of free existence grappling on 

 to a hair on the crab's body by means of hooks on its antennae. 

 The commonest species in this country is S. carcini para- 

 sitic on C. moenas ; S. neglecta on Inackus mauritajiicus is 

 frequent in the Mediterranean (Naples). 



Decapoda. — A considerable amount of knowledge has 

 been amassed with regard to the development of species of 

 Decapoda of economic value (Herrick, 1895, Williamson, 

 1904, Pearson, 1908, etc.). We are only able to notice here 

 the very broadest features ; details can be sought in the 

 literature above mentioned. 



According to Pearson (1908), fertilisation of Cancer 

 pagurtis takes place in the inshore waters during late 

 summer and autumn and is eff^ected immediately after the 

 female has cast. The spermatozoa remain in the openings 

 of the oviducts or spermathecse and the eggs are fertilised 

 during extrusion. The one supply of sperms is probably 

 sufficient for two or even three successive batches of eggs. 



The larvae of the Galatheidae, which include the familiar 

 " hermit lobster " (Galathea), and the porcelain crabs 

 {Porcellana platycheles and P. longicornis), are distinguished 

 by the enormous length of the spines upon the carapace, 

 regarded by some as an adaptive feature which renders their 

 ingestion by enemies a matter of difficulty. 



Hermit crabs pass through a zooea stage and a stage 



