of the Larva of the Marine Ci uslacea. 1 1 



situated at their base. Each 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-oesopliageal commissure, place this organ in 

 comnmnication with the thoracic portion of the central nervous 

 system. These two cords, which are exceedingly short in the 

 larvae of the Prawns, Porcellan<3e, Maice, Portuni, &c., and rather 

 more extended and thickened in the Lobsters, are excessively 

 long and slender in the Phyllosonies, 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 larvse of the Palinuri 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 Porcellunee, scarcely perceptible 

 furrows mark their separation. Each of these ganglia 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. 



In the Phyllosomes 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 ganglia 

 is excessively unequal, being 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 likewise 

 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 



