PODOPHTHALMIA. 47 



closely-grouped cephalic organs of Insecta. The Maioid species are 

 placed in the first rank by Edwards, and all facts sustain them in 

 this position. Here we find the eyes and the two pairs of antennae 

 brought most intimately into conjunction. The narrow front of the 

 species (unlike the broad Cancer), concurs to this end. The eyes, 

 moreover, extend in deep orbits, nearly to the medial line; and 

 directly beneath them, in the same line, lie the two pairs of antennae; 

 the inner on a narrow, longitudinal space, and the outer close along- 

 side. The mouth-organs are much more posterior; and here Crusta- 

 cea diverge from the Insecta. The Maioidea are then the highest, as 

 well from the organs of the senses, as the grouping of the thoracic 

 ganglia. 



This concentration is farther seen in the complete coalescence be- 

 tween the base of the outer antennae and the shell below. 



It is also observed in the insignificant size of the flagellum of these 

 antennae. With a highly sensitive nervous system, a long external 

 appendage is not necessary. Such an elongation of these organs is to 

 be found only as we descend in the scale. Among the Macroura 

 there is the largest development, and there is often an appendiculate 

 scale or lamella, by which the surface is still more enlarged. 



Passing from the Maioidea, to the Cancroidea, we find the eyes and 

 antennae still almost as nearly in the same transverse line ; the outer 

 (or second) antennae are, however, a little more posterior, and the 

 inner are almost always transverse, instead of longitudinal, separating 

 widely the outer antennae. The eyes, moreover, are more distant at 

 base. We detect, therefore, less evidence of the concentration pointed 

 out in the Maioidea ; — there is a partial dispersion of the forces which 

 are most energetic when so grouped together as to add the force of 

 each to all, with combined effect. Besides this, the base of the outer 

 antennae is bounded by a distinct suture on the outer side, instead of 

 being soldered to the shell, and in some cases of lower grade, this first 

 joint is quite free, and may even have motion. The abdomen and 

 sternum is still narrow, as in the Maioidea. 



These observations would place the Cancers highest among the Can- 

 croidea, since these species have the antennary space narrow, and the 

 inner antennae longitudinal, — and the Portunidae or swimming species 

 low, as here the outer antennae are often free at base. 



In the Geapsoidea, which follow next as a class, the eyes are usually 



