Crustacea.] SUBANTARCTIC ISLANDS OF NEW ZEALAND. 613 



they are folded back in Munida subrugosa, while they are kept extended in Grimothea 

 gregaria ; and these positions are naturally associated with the difference in habit 

 of the two forms. 



It is true that specimens with the external maxillipedes proportionally short 

 and in-folded as in Munida subrugosa are sometimes found which are no larger 

 than some of the specimens of Grimothea gregaria; and, on the other hand, large 

 specimens which from their size should belong to Munida subrugosa are also met 

 with which have the external maxillipedes elongated and showing the flattened 

 and foliaceous form characteristic of Grimothea gregaria. This has already been 

 recorded by Mr. Thomson when he says, " In several large males of Munida the 

 joints all show the flattened and foliaceous form characteristic of Grimothea, as well 

 as the densely fringing setae, while in one large female the joints are completely 

 foliaceous." Mr. Thomson speaks of these large forms as belonging to Munida, 

 and in another place, speaking of the small Grimothea form, he says, " Though I 

 have examined hundreds of individuals, I have always found the sexual appendages 

 in a more or less undeveloped condition." Prom the " Nora Niven " collections I 

 have a number of specimens varying from about 25 mm. in length to 54 mm. ; all 

 of these have the external maxillipedes more or less flattened and foliaceous, 

 though their length as compared with the length of the body seems to decrease 

 a little in the larger forms ; many of these large forms, however, varying from 

 35 mm. to 40 mm. in length, are mature females bearing eggs, and would un- 

 doubtedly be considered as belonging to Munida subrugosa but for the character of 

 their foliaceous maxillipedes, and it is doubtless large specimens of this kind which 

 Mr. Thomson had before him when he made the statement in the first sentence 

 quoted above. 



Considering these facts, it would no doubt be the simplest plan to say that there 

 are two species, differing in the form and size of the external maxillipedes, and this 

 is what has been done by Filhol and others. The general resemblance, however, 

 between the forms is so great, and the length of the external maxillipedes varies 

 so much in each form, that I cannot bring myself to agree with this view, but con- 

 sider we are dealing, after all, only with two forms of one species ; and this view 

 seems to be confirmed by the fact that where one form is met with in any particular 

 locality the other is also found somewhere in the neighbourhood. It is, of course, 

 only natural that the immature form should be pelagic in habit, while the mature 

 form inhabits the bottom of the sea ; and it seems likely that in this case, 

 just as in some other well-known animals, the immature stage may under certain 

 circumstances be prolonged, and even become sexually mature without com- 

 pletely losing its immature characters. I consider, then, that the foliaceous 

 maxillipedes of Grimothea gregaria are associated with its pelagic habit, and 

 that in the absence of favourable circumstances {e.g., a suitable sea-bottom 

 at moderate depth) it may continue pelagic, increase in size, and even become 

 sexually mature without losing its foliaceous maxillipedes ; but if it reaches 

 a suitable locality it adopts a more sedentary life at the bottom of the sea, 

 and in subsequent moults the external maxillipedes tend to become shorter and 

 less foHaceous and are in-folded instead of being kept extended as in the pelagic 

 form. 



