in the Ampliipoda. 369 



with two rows of long simple hairs," and specimens taken bj 

 myself in Sydney agree exactly with this description, while 

 those from Lyttelton Harbour differ in that these long simple 

 hairs are entirely absent, and in having the palm more di- 

 stinctly defined and more uneven, and the dactylos more 

 rounded at the end *. 



As Fritz Mliller says, " the occurrence of two kinds of 

 males in the same species may perhaps not be a very rare 

 phenomenon in animals in which the males differ widely from 

 the females in structure. But only in those which can be pro- 

 cured in sufficient abundance will it be possible to arrive at the 

 conviction that we have not before us either two different 

 species or animals of different ages"t- Ii^ view of this danger 

 I would like to point out that I have not as yet had a sufli- 

 cient number of specimens of Moera suhcarinata to make me 

 feel quite sure that the two forms are not simply animals of 

 different ages. I am the more doubtful in this case because 

 Mr. Walter Faxon has recently shown that what were con- 

 sidered to be dimorphic forms of the male in certain species 

 of Camharus are really " alternating periods in the life of the 

 individual, the ' first form ' being assumed during the pair- 

 ing-season, tlie ' second form ' during the intervals between 

 the pairing-seasons"^. 



In many genera of the Amphipoda, such as Mmra, Melita^ 

 Parancenia^ Podocerus, &c., the females of different species are 

 often much more alike than the corresponding males, which 

 usually have some of their limbs abnormally developed ; hence 

 if a supposed case of dimorphism or polymorphism occurs in 

 these genera it is more tlian usually difficult to decide whether 

 we have several species of which the females are alike, or nearly 

 so, or one species with several forms of the male to one of the 

 female. I have, however, an instance to bring forward from 

 the genus Microdeutero-pus^ and, though I have hesitated for a 

 long time, I think I have now sufficient evidence to show that 

 we have here a widely dispersed species which has three forms 

 of the male and only one of the female. 



In 1879 Mr. G. M. Thomson described a species of Micro- 

 deuteropus from Dunedin Harbour, giving it the name of M. 

 maculatus j at the same time he recorded the existence of 

 Aora typica in New Zealand, the species having been origi- 

 nally obtained at Valparaiso §, In a subsequent paper he 



* 'Transactions New-Zealand Institute,' xv. p. 82; 'New-Zealand 

 Journal of Science,' ii. p. 230; and 'Proceedings Linnean Society 

 N. S. W.' vol. ix. part 4, p. 1039. 



t ' Facts for Darwin,' p. 24. 



j ' American Journal of Science,' vol. xxvii. p. 42. 



§ Ann. & Mag. Nat. Hist. ser. 5, vol. iy. p. 381. 



