410 Dr. A. G. Butler on the Butterflies 



be free from error, and, furthermore, I am quite aware that 

 one should consider species and genera rather than groups. 

 But yet T venture xoitli due respect to direct attention to the 

 suhjecf in. the hope that zoologists who are dealing with pla^ik- 

 ton ifill not conjine their attention merely to the adult groups 

 of thp same, Imt will, in addition, arrange for the examination 

 of the larvoi therein in view of the distribution of the different 

 gt'oups of littoral animals. 



Considering eacli side of tlie question, remembering in 

 particular tlie faunas of oceanic banks, so far as we know 

 them, I venture to suggest that there are no banks to which 

 an abundant variety of Crustacean larva3 cannot pass, that 

 tlie maximum regular ])assage for Echinoderm (not Crinoid) 

 and Enteropnoust larvte is about twenty days, while for 

 Sipunculids, Annelids, Mollusca, and Crinoidea it is pro- 

 gressively less, the series passing on to Miiller's larva, 

 found in the Turbellaria, and ending with regular planulse 

 rot as a rule exceeding more than four or five days of oceanic 

 life, and probably in many forms averaging much less. 



Take the Cliagos Archipelago as a case in point. Crusta- 

 cean larvas should reach it freely from the Seychelles or 

 Africa and Australia, and the Crustacean faunas of the three 

 localities should be approximately the same for all forms of 

 the group possessing larval development. Many of the 

 Echinoderms and Enteropneusta should be common to the 

 Seychelles and Western Australian, but the Chagos forms 

 might reasonably be exj^ected to show some small variations 

 from their possil)ly parent stocks on either side. These 

 differences should be progressively more important in Sipun- 

 culids, Cha^to])n(ls, and Echiuroids, while the corals and 

 Tnrbellaria should have no more resemblance to those of the 

 Australian than to those of the African shore, and should 

 for the most part, indeed, have begun to take on forms which 

 are distinct varieties or subspecies of those found in the 

 Seychelles. 



Zoological Laboratory, 

 Cambridge. 



LV. — Tlie Butterflies of the Group Callidryades and their 

 Seasonal Phases. By Akthur G. Butler^ Ph.D., F.L.S., 

 F.Z.S., &c. 



Between the years 1*^97 and 1899 I revised a number of 

 genera of Pieridine Butterflies in the pages of the * Annals/ 

 and indicated their seasonal phases; but I unaccountably 



