MARINE BIOLOGICAL STATION AT PORT ERIN. 115 



called " Zoeas " (1) and are quite unlike the old crab. 

 They have a large jointed abdomen and several long 

 spines sticking out from the body. They swim freely on 

 the surface of the sea, and are frequently caught in the 

 tow-net in summer and autumn. After a time the Zoea 

 grows larger, casts its skin, and becomes the next stage, 

 or " Megalopa " (2) which is much more like a crab, but 

 has very conspicuous eyes (hence its name), and still uses 

 the out-stretched abdomen for swimming on the sea- 

 surface. The older Megalopa begins to haunt the sea- 

 weedy shores and may be found in rock pools, and so 

 gradually grows into the smallest size of crab. 



Several reports upon the crabs and other Higher 

 Crustacea, by Mr. A. 0. Walker, will be found in our 

 volumes. 



MOLLUSCA. 



(Figs. XXI. to XXIV.) 



The Molluscs, such as cockles and whelks, are the 

 true " shell-fish." They have no joints or segments, and 

 no legs, and the soft body is covered by a hard limy shell 

 which is generally in only one (univalve, such as whelk) 

 or in two (bivalve, as in oyster and cockle) pieces, the 

 valves. A few Molluscs, the sea-slugs (fig. XXIV.), have 

 no shell when adult ; while the Cuttlefishes have either no 

 shell, or a shell of a very special kind unlike that of 

 common univalves and bivalves. Figure XXL shows a 

 group of representative Mollusca. 1 is the large scallop 

 (Pecten maximus) with the rounded valve below and the 

 flat one above, the hinge where they join being at the 

 figure 1. Round the opening between the margins of 

 the valves is seen the soft edge of the body fringed with 



