10 M. Z, Gerbe on the Vascidar and Nervous Apparatus 



The venous circulation in the larvse, as in the perfect animals, 

 is rather lacunar than vascular. The blood which the arteries 

 have distributed to all parts of the body, returns indeed by 

 constant and determinate courses; but these courses consist of 

 a succession of cavities which the organs leave between them, 

 cavities in which it is difficult to ascertain the existence of 

 proper walls or of regular forms. Thus this mode of circulation 

 baffles description. All that can be said in a general way is, 

 that three principal perfectly limited currents, two anterior 

 and*-lateral and one posterior and median, open into the 

 heart. The two former, in the PhyllosomeSj are caused by the 

 fluids which circulate in the cephalic buckler alone ; the third 

 is formed by those which arrive from the true feet, the thorax, 

 and the abdomen. In the larvae of the other Macrurous Deca- 

 pods and in those of Brachyura, on the contrary, the fluids dis- 

 tributed to the head and thorax combine to form the lateral 

 currents, whilst the posterior current is produced solely by the 

 blood returning from the abdomen. 



The elements of the blood in the first age of the Crustacea 

 consist of a perfectly colourless liquid, and small, isolated, dia- 

 phanous corpuscles, some oblong or square, others angular or 

 virguliform, with the outlines very distinct, but always very 

 irregular, even when these kinds of globules affect a more or less 

 rounded form. 



Nervous Apparatus. — The nervous system of the larvse of the 

 Crustacea is composed, like that of the perfect individuals, of a 

 double series of ganglia or medullary masses, in which the 

 nerves of all parts of the body terminate. United to each other 

 by longitudinal cords, these ganglia, which are the more volu- 

 minous in proportion as the organs of the life of relation to 

 which they correspond are more developed, form a continuous 

 system upon the median line, extending from the base of the 

 ocular peduncles to the last joint of the abdomen. Neverthc' 

 less, taking into consideration the regions occupied by it, the 

 central nervous apparatus may be divided into a cephalic, 

 thoracic, and abdominal portion. 



The cephalic portion, or brain properly so called, is composed, 

 both in the Fhyllosomes and in the Zo'e'ce and other larvse of 

 Macrurous and Brachyurous Decapods, of a single ganglionic 

 mass, situated between the bases of the rudimentary antennae 

 and symmetrically divided into three unequal pairs of lobes, 

 each of which furnishes a sensorial nerve. From the two 

 anterior lobes spring the optic nerves, which pass directly into 

 the ocular peduncles ; from the two middle ones arise the inner 

 antennary nerves, and from the two posterior the nerves which 

 are distributed in the outer antenna and to the auditory organ 



