THE PENEUS. 46 1 



branch short and simple, the outer one longer, annulated at the 

 end, furnished with long setae, and kept, as in the genus Mysis, in 

 constant whirling motion. 



During this Alysis period the hearing organs are formed in the 

 base joint of the anterior antennae ; the inner branches of the first 

 three pairs of feet are developed into chelae, or pincers, and the two 

 hinder pairs into walking feet ; palpi sprout from the mandibles, 

 branchiae on the thorax, and swimming feet on the abdomen. The 

 spine on the labrum becomes reduced in size. 



In this way the animal gradually approaches the prawn form, 

 in which the median eye has become indistinct ; the spine of the 

 labrum and the outer branches of the cheliferous, pincer-bearing, 

 and walking feet have been lost, the mandibular palpi and the 



MYSIS FORM OF THE SAME PRAWN. 

 Magnified 45 diameters (after F. Miiller). 



abdominal feet have acquired distinct joints and sets, and the 

 branchiae come into action. In noticing the development of the 

 genus Mysis, F. Miiller states that the first organ which shows 

 itself in the embryo within the e^gg is the tail ; then more ap- 

 pendages on the other end, and the rudiments of antennae and 

 mandibles appear ; but the Q:g^ membrane bursts, and the animal 

 is set free, before any internal organ, or even any tissue, except 

 the cells of the skin, is formed. The Mysis is developed within 

 this skin bag. 



The Spiny Lobsters (the PalintiridcB) are not only well-known 

 articles of food, but are exceedingly interesting on account of 

 their strange transformations during development — transformations 

 much greater than those of the ordinary lobsters. There is one 

 species in the European seas, and its metamorphosis has been 



