CHAP. VII. ZOftJE OF TKUE CRABS. 51 



The Zoeae of the Crabs (fig. 17) are usually distin- 

 guished by long, spiniform processes of the carapace. 

 One of these projects upwards from the middle of the 

 back, a second downwards from the forehead, and fre- 

 quently there is a shorter one on each side near the 

 posterior inferior angles of the carapace. All these 

 processes are, however, wanting in Maia according to 

 Couch, and in Eurynome according to Kinahan; and 

 in a third species of the same group of the Oxyrhynchi 

 (belonging or nearly allied to the genus Achseus) I also 

 find only an inconsiderable dorsal spine, whilst the fore- 

 head and sides are unarmed. This is another example 

 warning us to be cautious in deductions from analogy. 

 Nothing seemed more probable than to refer back the 

 beak-like formation of the forehead in the Oxyrhynchi 

 to the frontal process of the Zoea, and now it appears 

 that the young of the Oxyrhynchi are really quite 

 destitute of any such process. The following are more 

 important peculiarities of the Zoeae of the Crabs, 

 although less striking than these processes of the cara- 

 pace which, in combination with the large eyes, often 

 give them so singular an appearance : the anterior 

 (inner) antennae are simple, not jointed, and furnished 

 at the extremity with from two to three olfactory fila- 

 ments; the posterior (outer) antennae frequently run 

 out into a remarkably long spine-like process ("styli- 

 form process," Spence Bate), and bear, on the outside, 

 an appendage, which is sometimes very minute ("squami- 

 form process " of Spence Bate), corresponding with the 



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