146 THE DEVELOPMENT OF 



Stage D (fig. 14) is characterized by the appearance of 

 the mandibles (///), the increase in size of antennulse 

 and antennee (/i), the indications of the supracesopha- 

 geal and optic ganglia, the larger size of the abdomen and 

 the appearance of the riidiments of the heart and dorsal 

 vessel, d, There is no longer a large space between 

 the labrum and the tip of the abdomen, and the latter ex- 

 hibits traces of segmentation. Both pairs of antenuie are 

 in front of the mouth. 



Stage E is another step in advance (ügs. 15 and 16) in 

 which the most marked features are the development of 

 four pairs of appendages behind the mandibles, making 

 seven in all (a number which persists for some time) and 

 the biramose condition of the second antennae {II), The 

 proctodeeum is also visible, although it was formed in the 

 preceding stage. 



Thls accoimt varies considerably from that of other ob- 

 servers on the early stages of decapods. For instance, 

 Keichenbach ('86) describes the mandibles as the first 

 appendages to appear and then the antennulse and lastly 

 the antennse,^ thus arriving at the so-called nauplius 

 stage. Likemyself (c/, '86, pl. IIa, fig. 7a, "Z6" et 

 ^^EIV) he has all the appendages at first distinctly postoral, 

 while he does not find that the mouth is distinctly behind 

 the antennse until a stage (his "G^") comparable to my 

 stage E, This primitively postoral position of all the 

 crustacean appendages has now been too firmly settled to 

 adniit of dispute. Ishikawa has the mandibles appear 

 first in Atyephyra, but thls, as explained above is, I think, 

 a mistake. 



There is one feature in the history which has already 

 been detailed to which attention should be called. A com- 



iReicheubach regards the Ophthalmie etalk as an appendage homonomous 

 with the rest, hence there is a discrepaiicy of one in tlie nomenclature of our 

 plates. 



