vin AETHEOPODA 177 



CEUSTACEA 



Classification adopted 



(The new terms invented by Caiman (1909) have not been universally adopted. 

 They are given in brackets.) 



. fBranchiopoda 

 I. Phyllopodai n . . 



{ Cladocera 



II. Cirripedia 



III. Ostracoda 



IV. Copepoda 



V. Malacostraca 



Leptostraca (Phyllocarida) 



Anaspida (Syncarida) 



Stomatopoda (Hoplocarida) 



flsopoda 

 Arthrostraca- Anisopoda 



[Amphipoda \ . . . . (Peracarida) 

 Cumacea 



I Mysidacea 

 Sckizopoda { , 



( Euphausidacea 



fPenaeidea 

 Caridea 



Decapoda 



Macrura 



Anomura 

 Brachyura 



Nephropsidea 

 \Loricata 



(Eucarida) 



When we now turn to survey what is known of the development 

 of other Arthropoda we find that Insects and Arachnida exhibit, 

 clearly and obviously, a comparatively slight modification of the type 

 of development exemplified by Peripatus. But Crustacea have a 

 development which is not so obviously referable to this type. One 

 or two Crustacea are said to have total segmentation of the egg. The 

 best known case of this is the Penaeid shrimp Lucifer as described 

 by Brooks (1882). With these exceptions the eggs of all Crustacea, 

 Myriapoda, Insecta, and Arachnida have incomplete segmenta- 

 tion, and all, including those which have total segmentation, have 

 the peculiar disposition of yolk known as centrolecithal. 



The eggs of Peripatus capensis and of allied species are the only 

 Arthropodan eggs which could properly be described as telolecithal. 

 In a centrolecithal egg the yolk is densest in the interior of the egg, 

 and it is surrounded by a skin or rind of cytoplasm. Often the 

 nucleus of the ripe egg is situated near the centre in a sort of island 

 of . cytoplasm, but when it divides the daughter nuclei wander 

 outwards and take up their places on the exterior; consequently a 

 segmentation of the egg results which is apparently total but is in 

 reality superficial, for the cleavage planes dividing the blastomeres 

 from one another extend only a limited distance inwards, so that 



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