Royal Microscopical Society. 105 



ible and pointed : the sarcodous part or tail stretches out for more 

 than the length of the caput, and consists as usual of a very finely 

 granular protoplasmic material ; it is thick and undivided, not pre- 

 senting the branches which were found in P. Bernhardus. The 

 length of the caput is generally about • 006 mm,, the breadth about 

 0-004 mm.; the rays measure about 0"016 mm. in length, while 

 the tail is ■ 008 mm. The stages of development in this species 

 resemble those in P. Bernhardus. Fig. 2 gives a representation of 

 zoosperms which are not quite mature ; the tail has not yet appeared ; 

 the rays are shorter, and the caput is larger than when they arrive 

 at their full growth. The animal itself was very plentiful in the 

 Bay of Spezia, and many specimens presented an interesting instance 

 of commensalism ; some of them inhabited a shell much too small for 

 them, fomiing in fact but o. point d'appioi for the end of the abdomen, 

 the rest of their protection being afforded by a dense red sponge, 

 which externally formed a rounded mass shaped like a pebble, and 

 internally was excavated into a smooth passage adapted to the shape 

 of the crab. Both these animals had evidently grown old together, 

 and the hermit finding the sponge to form such an efficient shelter, 

 had not thought it worth while to change its abode, as is the custom 

 with the rest of its congeners. 



Another small species of hermit crab from the same locahty, 

 which I take to be P. callidus, is provided with zoosperms, the 

 capita of which are more robust than those of P, maculatus. The 

 contour is usually dome-shaped ; but sometimes it approaches to a 

 quadrangular form with the anterior angles rounded off. Across 

 the base there runs a ridge of refracting material which makes this 

 part square in some cases, while in others a portion of the softer 

 substance which appears to occupy the centre projects beyond the 

 ridge, which then does not form the limit of this part of the 

 zoosperm. There are three sharp and flexible rays, as in the last. 

 The tail or soft appendage varies much ; in some specimens it 

 is short and thick, in others it is long and thin, while others present 

 every gradation between the two extremes. In this species the 

 appendage looks like a thick walled bag attached to the base of the 

 caput, composed of the same kind of material as in the P, maculatus. 

 Fig 3 gives a representation of them. In size they are a trifle 

 larger than those of P. maculatus. 



In P. ornatus, another small species which I found at Leghorn, 

 the zoosperms are gigantic in comparison with those of P. callidus, 

 P. maculatus, or P. Bernhardus, and there is nothing in the size of 

 the animal to account for this difference, as it is much smaller than 

 the latter species, and no larger than the two former. This shows 

 that zoosperms, like blood corpuscles, have no relation to the bulk 

 of the body. In shape the zoosperms in this species are oval, in some 

 cases with the sides slightly flattened, "When first placed on the 



I 2 



