166 CRUSTACEA—_EUGARIDA——DECAPRODA CHAP. 
soma, which must be regarded as a greatly flattened and modified ' 
Mysis stage. 
In the embryo of Palinurus just before hatching (Fig. 112) 
we can recognise the limbs of the head and thorax normally 
developed in order. There are present three thoracic limbs, 
besides the maxillipedes. 
When the Phyllosoma 
hatches out the first 
maxillipedes have _ be- 
come quite rudimentary, 
and the second much re- 
duced, while the second 
antennae and second 
maxillae are also re- 
duced) “in: “size? a=) the 
metamorphosis is com- 
pleted by the re-develop- 
ment of the lmbs and 
Fig. 113.—Phyllosoma larva of Palinurus, sp. x 5. 
Ab, Abdomen; Map, 3rd maxillipede; 7, ante- segments that have 
pe aumiake (6th) thoracic appendage. (After been secondarily sup- 
eet pressed during — larval 
life, and by the appearance of the pleopods. 
This process is again met with in the Squillidae (p. 143), 
but it resembles the suppression, in so many Decapodan meta- 
morphoses, of anterior limbs and the precocious development of 
segments and limbs lying posteriorly. In the ordinary Decapoda, 
however, the suppressed limbs are merely not formed till later ; 
while in the Loricata the limbs develop in the correct order, and 
subsequently degenerate. It is natural to wonder whether the 
condition of affairs in the Loricata represents the primitive 
process, and whether the precocious development of segments in 
the other Decapoda owes its origin to these animals having once 
had the direct mode of development when the segments were 
formed in the proper order, and to their having subsequently 
acquired the larval stages first of all by the degeneration, and 
then by the suppression of certain segments which were not of 
use during larval life. The complete metamorphosis, however, of 
the Peneidea, in which the segments and limbs appear in the 
1 Claus, Unt. 2. Erforschung d. genealog. Grundlage d. Crustaceensystems. 
Vienna, 1876. 
