70 



L. A. BORRADAILE. 



Fig. 14. Left Antennules 



A. Eupagurus bi'rnhardus 



B. Coenobita clypeatus. 



The fore-part of the cephalothorax is strongly compressed, having a narrow, vaulted roof 

 and flat vertical sides. Its compression extends also to the antennae and the first three 

 pairs of legs, enabling the whole comple.x, including the limbs, to be withdrawn into shelter 

 when necessarJ^ The absence of the rostrum is, no doubt, an adaptation to the same 

 end. The cuticle over the whole of these exposed structures is strongly calcified. 



The eyestalks are narrow and elongated and directed straight forwards above the anten- 

 nules ; the eyes themselves are small. Some rather abnormal 

 features appear in the antennules (fig. 14). By the lengthening of 

 their joints, the stalks of these appendages far outreach those 

 of the antennae, bearing at their ends each a long and a short 

 flagellum, the whole being able to be folded up lengthwise and con- 

 cealed under the body. The long flagellum, which is the more 

 dor.sal of the two, is compressed and club-shaped, with a blunt, 

 rounded end. Its lower edge is covered, in the distal two-thirds, 

 with a close fur of short "olfactory" hairs'. The short flagellum 

 tapers at the end, and bears on the penultimate joint a long 

 bristle, which looks as if it were adapted for cleaning the olfactory 

 hairs of the long flagellum. The opening of the otocyst is small, 

 but situated in its usual position on the dorsal side of the basal 

 joint of this limb. The antennules of the Pagurids (fig. 14), on 

 the other hand, are relatively short, and bear each two short flagella, like those of the 

 crabs. The dorsal (outer) flagellum tapers to a point and bears below a fringe of olfactory 



hairs much longer than those of Coenobita. These pecu- 

 liarities of Coenobita are perhaps in connection with the 

 habit of exercising the sense of smell in the search for 

 food^, and that in a different medium from the one in 

 which the Paguridae live, while at the same time it is 

 necessary that the organs be able to be withdrawn into 

 a small space. 



The scale of the antenna (fig. 15), which in the 

 Pagurids is well developed and moveable, is, in Coenobita, 

 reduced in size and, except in one instance^ fused with 

 the second joint of the flattened stalk of the limb. The 

 flagellum ends bluntly instead of tapering to a point 

 like those of most mai-ine Decapods — a feature, which 

 must probably be attributed to the same cause, which 

 has shortened the sensory hairs of the antennule. The 

 Fig. 15. Left Antennae. A. Eupagurus mouth-limbs (fig. 16) present no remarkable features. 



bernluirdus ; B. Coenobita clypeatus ; C. „, ^^ j_ ^ i i ^ i ^ j i 



_ , ., , , 1 » i 1 , .1 Ihey are all stout and show a tendency to develope 



Coenobita perlatus. 1. Antennal scale. 2. ■■ j r 



Tubercle with opening of green gland (not tufts and fringes of strong, close set, hairs. The powerful 

 seen in A). cutting edge of the mandible is not toothed, and the lash 



of the exopodite of the first maxilliped is wanting. 



' The statement of Ortmann [Bronn's Thierreich, v. 2, matted in the absence of a supporting medium such as water, 



p. 1146] that these appendages "laugen Sinneshaare ent- is no doubt an adaptation to terrestrial life, 

 behren" is thus somewhat misleading, though strictly true. - See below, p. 92. 



The shortness of the hau-s, which would be apt to become ^ C. clypeatus, Latr. 



