220 DISCOVERY REPORTS 



shrunk to a very great extent and has lost the whole of its plumose setae. Its shape is ill 

 defined and irregular and it appears merely as a lobe at the extremity of the proto- 

 podite. The endopodite is also very much smaller than before and it now projects like a 

 horn a little way down the inner border of the protopodite. The pleopods of the third to 

 fifth abdominal segments have this form, but that of the second abdominal segment has 

 altered to a more marked degree and the ultimate simple two-segmented female form is 

 already strongly foreshadowed. The protopodite, carrying no setae, is much smaller 

 than in the succeeding pleopods and the endopodite and exopodite project from the end 

 as two lobes, the exopodite being the more prominent (Fig. 4/?). Specimens of this 

 stage preparing for ecdysis and identified as M. gregaria, showed the flat, foliaceous 

 pleopod of the next stage so outlined as to demonstrate that the original exopodite 

 would be suppressed and the endopodite retained (Fig. 47). 



When this ecdysis is completed, the third, fourth and fifth pleopods are flat and ex- 

 panded (Figs. 5«-c). The inner edge is straight or slightly concave, whilst the outer is 

 convex and carries articulating plumose setae to the number of nine to twelve. This is 

 the part corresponding to the protopodite of the earlier biramous pleopod. Articulated 

 to this, at the junction of the inner straight and outer curved borders, is the relic of 

 the endopodite appearing as a simple, short projection, the exopodite having entirely 

 disappeared. The appendage of the second abdominal segment (Fig. ^d) consists merely 

 of a two-segmented process of a very simple nature. 



The foregoing account describes the course of growth in both sexes, but at this stage 

 in the male the development of the third to fifth pleopods is arrested except for pro- 

 gressive increase in size. The pleopods of the second segment together with those of the 

 first, which have yet to appear, metamorphose to become the copulatory appendages 

 before the adult form is fully realized. 



The pleopods of the female, with the exception of those of the second segment, which 

 already have almost their final shape, have to become modified considerably in order to 

 attain the adult egg-carrying form. This form is attained by the loss of the lobe of the 

 protopodite, by extension of the endopodite and by a considerable lengthening and 

 stiffening of the whole limb, together with the growth of hairs to which eggs will be 

 attached. Perez (1927) has described this post-larval metamorphosis of the female 

 pleopods in Galothea and states that the same change takes place in Munida. He says 

 that the small finger-like terminal process of the protopodite is composed of two segments 

 in the male, whereas in M. subrugosa it is composed of only a single segment ; and, 

 though giving no evidence for his statement, he asserts that this is a rudimentary 

 endopodite. The process is in fact an endopodite, but it should rather be looked upon 

 as a degenerate endopodite, whilst the exopodite has been completely aborted. Selbie 

 (1914) mentions male Galathea intermedia with this endopodite composed now of one 

 segment and now of two. 



In our species the change in the form of the female limbs takes place from the most 

 posterior segment anteriorly, as though the centre of the metamorphic activity were 

 situated in the fifth abdominal segment and gradually extended forward. When the 



