DECAPOD A. 257 



The Mysidac, ike Nehalia, only undergo metamorphosis within the brood- 

 cavity of the mother, the young which leave that cavity already showing the 

 form of tlie adult. We have mentioned above (p. 154) that the egg-integument 

 in Musis is shed at the Nauplius stage. The larva, which is then enveloped in 

 the Nauplius cuticle alone, is essentially embryonic in character. It is maggot- 

 shaped and can move but little, the limbs are soft and have no fringe of setae. 

 The larval cuticle, beneath which the remaining limbs develop, is distinguished, 

 in Mysis vulgaris and M. fiexuosa, by the fact that, at its posterior end, it runs 

 out into two setose furcal processes. The next ten pairs of limbs (two pairs of 

 maxillae and eight pairs of thoracic limbs) appear simultaneously. The first 

 of the pleopoda to appear is the sixth pair which enters into the formation of 

 the caudal fin (Fig. 77 E, p. 153) ; the five anterior pairs grow out only after 

 the shedding of the Nauplius cuticle (P. J. and E. Van Beneden, Nusbaum). 



The coui'se of development in the LopJiogastridae seems to be in comjjlete 

 agreement with that in the Mysidac. Sars, at least, has figured an ontogenetic 

 stage of LopJiogasfer, which completely resembles a late larval stage of Mysis, 

 the only distinction being that, in the former, all tlie pairs of pleopoda are 

 already present ; these limbs perhaps appearing somewhat earlier in Lopho- 

 gaster than in Mysis. 



The development of the Mysidae and the Lophogastridae may in a general way 

 be described as essentially abbreviated in comparison with that of the Euphau- 

 siidae. In this respect, as well as in the inner ontogenetic processes, the Mysidae 

 and Lophogastridae approach the Cumacea and the Arthrostraca. 



10. Decapoda. 

 A. Sergestidae,* 



Among the Decapoda, the Sergestidae and the Penaeidae are 

 distinguished by the primitive conditions recalled by their meta- 

 morphoses, Avhich begin with a very simple stage [Nauj?Hus or 

 MetanaiipHus), and also by the regular order of appearance (from 

 before backward) retained by the body-segments. 



In the family of the Sergestidae, the metamorphosis of the genus 

 Lucifer has been specially accurately observed. The Protozoaea of 

 this ontogenetic series was called by Dana Eridhina demissa ; 

 Claus (No. 8) afterwards found the Zoaea stage belonging to it, 

 but WiLLEMOES-SuHM (No. 157) first established its connection with 

 the development of Lucifer, while Brooks (No. 109) observed the 

 complete course of metamorphosis, from the hatching of the egg to 

 the attainment of the adult form. His observations have been 

 found to agree with those made on the Challenger material by 

 Spencb Bate (No. 100) and Willemoes-Suhm. 



The actual Naiqjlius stage is passed through in the &gg; the young 

 Lucifer larva hatches at a stage which we must describe as a Meta- 

 nauplius (Fig. 118 ^). On the short oval body we can recognise the 



* [The Sergestidae and Penaeidae form the tribe Penaeidea comparable to the 

 Caridea, etc. — Ed,] 



8 



