REPRODUCTION AND GROWTH 269 



equivalent to a megalopa. The former differs from that of 

 the Galatheidse in the absence of the long spines. 



Among the Brachyura generally the following larval 

 stages may be distinguished : Protozooea, Zocea (4 kinds), 

 Megalopa (Pearson, loc. cit.). The general appearance of 

 Zocea and Megalopa can be seen from the illustrations 

 (Plates III and XIV). The Protozocea differs from the later 

 zocea only in the absence of the spines on the carapace. 



The larva of the lobster {Homarus vulgaris) is a My sis, 

 that is to say, it is very much like the adult except that the 

 thoracic limbs are biramous. After five or six months of a 

 free-swimming existence during which it moults 4-5 times, 

 the animal, now exactly like the parent except for size(|^ inch), 

 sinks to the bottom. The breeding season of the lobster 

 extends over July and August. A female lobster begins to 

 lay when she is about eight inches in length, the number 

 of eggs produced increasing up to about 180,000 at eighteen 

 inches, after which there is a gradual decrease. 



Like that of the lobster, the metamorphosis of prawns 

 and shrimps is greatly abbreviated, the larva hatching out 

 at a late zocea stage (almost a Mysis). According to Monaghan 

 (1914), the time of maximum spavming of the shrimp 

 {Crangon vulgaris) for the Lancashire coast is about April loth. 



The larva of the spiny crayfish (Palinurus), which takes 

 the place of the lobster on Mediterranean coasts, is known 

 as a Phyllosoma and is characterised by its leaf-like body 

 and flattened appendages. It may be regarded as a greatly 

 modified Mysis stage. Lovett (1901) remarks that while 

 the spiny lobster Palinurus quadricornis carries enormous 

 numbers of ova of very small size in proportion to the parent, 

 Callianassa subterranea produces ova which, though large, 

 are few in number. As, however, the latter species is 

 greatly protected by living underneath ;he sand such 

 disparity is accounted for. 



Amphipoda and Isopoda. — Sex-union in this group, 

 particularly the former, may be readily observed, the male 

 cariying the smaller female beneath him by means of the 

 anterior thoracic legs for a considerable period (several days). 



