2i8 DISCOVERY REPORTS 



This may or may not be the last larval stage, but comparison with the last stage of 

 M. banffica makes it very probable that a post-larval form follows. If the foregoing 

 five stages can be looked upon as separate and comparable with the four stages of 

 M. banjfica, a further resemblance to Galathea, where five stages are known at times to 

 occur, is presented. A certain amount of variation occurs within each stage, principally 

 in the number of hairs on the antennal scale. 



The post-larvae, apart from one or two structures which have yet to be modified, 

 such as the pleopods, have the form of the adult. In consequence of their small size 

 distinction between the two species is difficult at first, but the difference in the length 

 of the eye stalk and the modification of the third maxillipedes in M. gregaria soon be- 

 come apparent. The rostrum has not at first a single point as in the adult, but in the 

 earlier post-larvae the tip of the rostrum has the appearance of a trident with the two 

 lateral spines longer than the central spines. Later, the central spine is increased in 

 length and the two lateral spines become subsidiaries, whilst other small spines have 

 made their appearance along the sides of the rostrum. In the Grimothea stage of M. 

 gregaria many more lateral spines have arisen, giving to the edges of the rostrum a 

 toothed appearance ; from the base of each tooth springs a single, short, stiff hair. These 

 lateral teeth are retained in the adults of both species, but with the greatly increased 

 size of the rostrum they become overshadowed and insignificant. 



DEVELOPMENT OF PLEOPODS IN MUNIDA SUBRUGOSA 



The appearance, in the fifth larval stage, of the pleopods on the abdominal segments 

 as very simple biramous appendages has already been mentioned above. Later, in the 

 early post-larval stage, when the young M. subriigosa has acquired the general adult 

 structure, the pleopods of the second to fifth segments still display the biramous form, 

 thus differing considerably from the adult of either sex. The typical pleopod at this 

 stage, when the carapace has a length of 3-4 mm., consists of a large stout protopodite 

 carrying an endopodite and an exopodite (Figs. ^a-d). The endopodite is a small, 

 simple segment attached to the inner distal corner of the rectangular-shaped proto- 

 podite. The expodite, on the other hand, is much larger and carries about fourteen long, 

 strong and heavily plumose setae. Two of these are arranged close together at the 

 extreme tip, and of the remainder six are placed along each side ; at times, five or seven 

 may occur instead of six. The setae spring from collars articulating with the exopodite. 

 The surface of the exopodite is sculptured with conchoidal depressions opposite these 

 articulations, giving the body of the exopodite, with its subconical shape, the appearance 

 of a pineapple. 



In the next stage examined (Figs. 4e-//) the pleopods have entirely changed in 

 character. Considerable reduction has taken place, although the size of the protopodite 

 is greater relative to the size of the exopodite and endopodite. The inner edge of the 

 protopodite remains straight, but the outer has become markedly convex and now 

 carries six to ten stout plumose setae. The exopodite has changed considerably. It has 



