58 K. ZIMMERMANN. 



against dangers of friction, etc., by the lateral branchiostegite flap of the 

 carapace, which loosely overhangs the cavity. The case of the Brachyura 

 is quite otherwise. These shore-living Crustacea are constantly exposed 

 to the dangers of life in the wave-washed zone, and protection against 

 one of the greatest of these dangers is ensured by the enclosing of the 

 branchial cavity by the strongly- curved branchiostegite. This leaves 

 only the following apertures : a pair at the posterior end of the carapace, 

 a pair at the bases of the chelae, a pair near the mouth — and, on each side, 

 a long chink, so narrow as to be practically inconsiderable, between 

 carapace and thoracic leg-bases. The first two pairs of apertures (en- 

 trance channels for the breathing current) are well guarded by a straining 

 apparatus formed by a fringe of hairs of very complex structure (Plate 

 4, G), while the aperture on each side of the mouth (an exit channel) 

 can be protected by the folding of the plate-like maxillipedes against the 

 body-wall. The fourth pair of apertures, mere chinks, are curtained by 

 a fringe of hairs bordering the branchiostegite and by the tufts of " coxo- 

 poditic setse." 



One might expect to find in Galatheidse a type of arrangement more 

 or less intermediate between these two extremes — the Macrurous and 

 the Brachyurous — and such is, in fact, revealed. Throughout the group, 

 the closing-in of the branchial cavity is far less complete than in the 

 Brachyura, although a curved and down-bent branchiostegite protects it 

 laterally, and the paired inhale nt aperture (posterior, near the bases of 

 appendages XII and XIII) is guarded by. a ring of hairs. Coxopoditic 

 tufts also prevent the entrance of mud through the longitudinal crack 

 between branchiostegite and leg-bases — which crack is far wider than in 

 Brachyura, the whole branchial cavity being wide in the vertical rather 

 than in the horizontal plane. 



Galathea, an active swimmer, has retained some of the epipodites so 

 characteristic of primitive Macrurous forms like Peneeus. In G. squami- 

 fera (common around our coasts), there are epipodites, fringed with 

 long and fairly simple hairs, on appendages VIII to XI (Plate 2, B, and 

 Plate 1, F). One important function of the epipodites, as established by 

 M. Bohn("Des mecanismes respiratoires chez les Crustaces Decapodes," 

 Bull. Sci. Fr. et Belg., XXXVI) is to brush the surfaces of the Arthro- 

 branch gills and sweep them clear of particles. With so efficient a sweep- 

 ing mechanism, it seems that elaborate precautions against the entrance 

 of mud are unnecessary : we find that in this species the guardian-hairs 

 which fringe the inhalent aperture are of the same fairly simple type as 

 those which occur along the whole of the carapace edge (Plate 7, B). 



