CRUSTACEA. 



469 



This is shewn in the following table compiled from Claus' observations. 



All the appendages following the second pair of maxillas are biramous, 

 and the first eight of these bear branched gills as their epipodites. It is 

 remarkable that the epipodite is developed on all the appendages anteriorly 

 in point of time to the outer ramus (exopodite). 



Although in Mysis there is no free larval stage, and the development 

 takes place in a maternal incubatory pouch, yet a stage may be detected 

 which clearly corresponds with the Nauplius stage of Euphausia (E. van 

 Beneden, No. 465). At this stage, in which only the three Nauplius 

 appendages are developed, the Mysis embryo is hatched. An ecdysis 

 takes place, but the Nauplius skin is not completely thrown off, and 

 remains as an envelope surrounding the larva during its later develop- 

 ment. 



Decapoda. Amongst the Decapoda the larva usually leaves 

 the egg in the Zoaea form, but a remarkable exception to this 

 general rule is afforded by the case of one or more species of 

 Penseus. Fritz M tiller was the first to shew that the larva of 

 these forms leaves the egg as a typical Nauplius, and it is 

 probable that in the successive larval stages of these forms the 

 ancestral history of the Decapoda is most fully preserved 1 . 



The youngest known larva of Penaeus (fig. 214) has a some- 

 what oval unsegmented body. There spring from it the three 

 typical pairs of Nauplius appendages. The first is uniramous, 

 the second and third are biramous, and both of them adapted 



1 The doubts which have been thrown upon Miiller's observations appear to be 

 quite unfounded. 



