of the Larve of the Marine Crustacea. 11 
situated at their base. Hach of these lobes likewise furnishes a 
pair of nerves running to the muscles and the integuments. 
Two cords issuing from the posterior lobe of the brain and 
united by an ante-cesophageal commissure, place this organ in 
communication with the thoracic portion of the central nervous 
system. These two cords, which are exceedingly short in the 
larvee of the Prawns, Porcellane, Maia, Portuni, &c., and rather 
more extended and thickened in the Lobsters, are excessively 
long and slender in the Phyllosomes, in which they also present 
a second commissure behind the brain. 
But it is especially in the arrangement of the ganglia of the 
thorax that the larve of the Palinurt are distinguished from 
those of other Decapods that I have been able to observe. In 
the latter, the thoracic nervous system, represented by the five 
pairs of ganglia related to the buccal appendages, and by the 
five pairs corresponding with the ambulatory feet, forms a 
single oblong mass, pierced at the level of the third and fourth 
pairs of true feet for the passage of the sternal artery—a mass 
in which the ganglia are so intimately connected that some- 
times, as for example in the Porcellane, scarcely perceptible 
furrows mark their separation. Hach of these gangha furnishes 
two pairs of nerves: one issues directly from the central medul- 
lary nucleus, the other appeared to me to be intimately con- 
nected with the nervous portion which forms the commissures. 
Their origin would therefore be different. 
Ini-the Phyliosomes the thoracic nervous system certainly 
forms a double chain as in the other species, but the ganglia, 
instead of being grouped in such a manner as to form a body, 
are, on the contrary, very distant from each other, their only 
communications being formed by rather long longitudinal and 
transverse commissures. Moreover the volume of these gangha 
is excessively unequal, bemg in relation to the development of 
those organs to which each of them corresponds. The masti- 
catory appendages, the first pair of footjaws, and the true feet 
of the fourth and fifth pairs being rudimentary or incomplete in 
the Phyllosomes, the ganglia devoted to these parts lkewise 
present themselves in a rudimentary state. 
The concordance which I have just indicated is still more 
manifest in the portion of the nervous apparatus which belongs 
to the abdominal region. ‘This region, where everything in the 
Phyllosomes is in the condition of a mere sketch (the segments 
of which it is composed, as well as the false legs of which 
the successive moults cause the appearance), instead of six 
pairs of ganglia which may be detected in ~it in individuals 
furnished with their abdominal appendages, presents nothing 
but the prolongations of the two nervous cords or longitudinal 
