SCHIZOPODA. 253 



shows the rudiments of all the thoracic limbs, not merely straightens 

 out, but becomes even somewhat dorsally curved. We thus have, 

 in Nehalia, a repetition of the changes with regard to the relative 

 position of the body regions which we saw (p. 154) commencing 

 in Mysis, but with the difference that, in the latter, the rupture 

 of the egg-integuraent and the straightening of the body take place 

 as early as the Nauplius stage, whereas here they occur at a later 

 stage. The pleopoda now gradually appear in regular order from 

 before backward, the body approaches the adult form, and the young 

 leave the brood-cavity (Metschnikoff, No. 82). 



9. Schizopoda. 



A very primitive form of metamorphosis through many moults is 

 retained among the Schizopoda by the Euphausiidae. The Mysidae, 

 on the other hand, emerge from the Nauplius cuticle 'in a condition 

 closely resembling the adult in form, and at this stage they leave 

 the brood-pouch of the mother and swim about freely (p. 1 53). 



The different larval stages of the Euphausiidae, none of which can 

 be exactly identified with the Protozoaea and Zoaea of the Decapoda, 

 were described by Dana as separate genera under the names of 

 Calypiopis, Furcilia, and Cyrtopia, Claus (No. 97) being the first 

 to prove that these forms belonged to the ontogeny of the Euphau- 

 siidae. The youngest stages were made known by Metschnikoff 

 (Nos. 93 and 94), who established the important fact that the larva 

 of Euphausia leaves the egg as a true Nauplius. The most important 

 points in the later ontogenetic stages were made known to us chiefly 

 by Claus (Nos. 91 and 8) for Euphausia, and more recently the 

 process of development in various forms has been traced in greater 

 detail by G. 0. Sars (No. 95), Brook and Hoyle (No. 90). 



The Nauplius of Euphausia, on leaving the egg, has an oval 

 unsegmented body still without a shell-fold, and carrying on its 

 anterior half the three pairs of typical Nauplius limbs. The anterior 

 pair of these is uniramose, the two others biramose ; their distal ends 

 are beset with setae. A segmentation of the limbs is not yet 

 distinctly evident. Only a very small oral aperture can be seen. 



Later stages (Fig. 117 A) are distinguished by the development of 

 three more limb-rudiments (two pairs of maxillae (4 and 5) and the 

 first maxillipedes), and must therefore be regarded as Metanaup/iu.< 

 stages. The three anterior pairs of limbs (1, 2, 3) have still the 

 Nauplius character. We can recognise the rudiments of the Nauplius 

 eye, the upper lip (o), the paired paragnatha (u), and a shield-like 



