Metamorphosis and Life-history of Gnathia maxillaris. 47 I 



brown and appear as conspicuous bodies in tlie hinder tliovacic re- 

 gion. This poiut is of considerable interest beeanse it gives us a 

 simple explanation of the reacquisition of segmentation in the male 

 and not in the female; for whereas in the male the food in the gut 

 is taken up and compactly stored in special organs for the purpose, 

 in the female the thorax beeomes filled with a mnltitude of embrvos 

 which naturally take np more room than the compact liver of the 

 male. But as we shall see the female mav reacquire its segmentation 

 if it is not very full of eggs: thin segmented females occuring as 

 rather rare varities. It will be noticed from this account that the 

 Statement of Korschelt & Heider (4) that unsegmented Pranizae 

 give rise exclusively to females and that only segmented larvae give 

 rise to males is quite erroneous. The adults of both sexes are 

 derived from swollen Pranizae. 



Metamorphosis of the Female. The change from the Praniza 

 iuto the adult female is not so dramatic as in the case of the male. 

 The mouth parts merely degenerate, except the first maxilliped which 

 resembles that of the male. 



The ova begin to develo]) at a fairly early stage in the Praniza 

 and are recognisable as a narrow strip rnnniug down the centre of 

 the back (fig. 1 o): they continue to grow at the expense of the 

 nourishraent in the gut and come to fili the whole of the body 

 cavity of the mother, when the final ecdysis occurs. Hesse supposed 

 that fertilization took place before the final ecdysis, but this was 

 merely a supposition, and although I bave been unable to observe 

 the coupling, the circumstantial evidence seems to show that the 

 supposition is wrong; at auy rate Hesse's contention that fertilization 

 is a necessary Stimulus for the accomplishment of the final ecdysis 

 is certainly erroneous, because I bave succeeded in rearing several 

 Pranizae to the adult female state, but in ali cases the eggs failed 

 to develop and subsequently decayed so that it is highly improbable 

 that the Pranizae had been fertilized. We bave already mentioned 

 that the female normally has the bind part of the thorax unsegmented 

 fas in fig. 8), but occasionally sjx'cimens are found with eitlier one 

 or both constrictions fully present (as in fig. 9) and these speciniens 

 are always thinner and coutain fewer eggs. They plainly belong to 

 the same species because they do not differ in any other morpho- 

 logical detail and they occur together with only one form of male. 



It is a remarkable fact that the embryos develop to a late 

 stage within the body cavity of the mother and completely destroy 



