146 THE DEVELOPMENT OP 



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

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

 and antennas ( II) , the indications of the supracesopha- 

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

 the appearance of the rudiments 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 antennae are 

 in front of the mouth. 



Stage E is another step in advance (figs. 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 

 proctodaeum is also visible, although it was formed in the 

 preceding stage. 



This account varies considerably from that of other ob- 

 servers on the early stages of decapods. For instance, 

 Reichenbach ('86) describes the mandibles as the first 

 appendages to appear and then the antennula3 and lastly 

 the antenna, 1 thus arriving at the so-called nauplius 

 stage. Like myself (cf, '86, pi. lla, fig. 7a, "&" et 

 "1212") he has all the appendages at first distinctly postoral, 

 while he does not find that the mouth is distinctly behind 

 the antenna3 until a stage (his "6r") comparable to my 

 stage E. This primitively postoral position of all the 

 crustacean appendages has now been too firmly settled to 

 admit of dispute. Ishikawa has the mandibles appear 

 first in Atyephyra, but this, 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- 



1 Reichenbach regards the ophthalmic stalk as an appendage homonomous 

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

 plate*, 



