THE PENEUS. 461 
branch short and simple, the outer one longer, annulated at the 
end, furnished with long sete, and kept, as in the genus JZyszs, in 
constant whirling motion. 
During this JZyszs period the hearing organs are formed in the 
base joint of the anterior antenne ; the inner branches of the first 
three pairs of feet are developed into chele, or pincers, and the two 
hinder pairs into walking feet; palpi sprout from the mandibles, 
branchiz 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 seta, and the 
branchiz come into action. In noticing the development of the 
genus J/yris, F. Miiller states that the first organ which shows 
itself in the embryo within the egg is the tail; then more ap- 
pendages on the other end, and the rudiments of antenna and 
mandibles appear; but the egg 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 Palinurid@) 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 
