190 EVENINGS AT THE MICROSCOPE. 



according as the perfectly hexagonal outline of each, 

 or the smooth and glossy convexity, comes into focus, 

 that is so peculiarly charming. 



Heturning now to the examination of one of the living 

 Zoeas, you perceive that the three pairs of pencilled 

 limbs do not represent any of the true legs; for the 

 transparency of the integuments allowing the interior 

 to be clearly seen, and the organs of the imago being 

 matured and just ready for sloughing, you discern, with 

 the most beautiful distinctness, the fingered claws (short 

 and stumpy, it is true, as compared with their perfect 

 form in the newly-freed imago) folded down upon the 

 breast within the skin, the second pair as large as these, 

 and traces of others beneath them, — all these forming 

 two great projecting lobes, slightly movable, beneath the 

 thorax of the Zoea, and occupying a bulk nearly equal 

 to that of the whole shield. 



The circulation of the blood is beautifully clear. The 

 pellucid colourless globules chase each other by starts to 

 and fro, as the eye rests on the outgoing or returning 

 current. It is distinct in some parts where you would 

 scarcely have looked for it; as all over the lozenge plate 

 of the tail, in the interior of the eyes, throughout the 

 posterior spines of the shield, and the frontal spine. But 

 besides, and apparently independent of, the circulation, 

 there is a singular fusiform vessel in the latter segments 

 of the abdomen, penetrating the tail-plate, on the ventral 

 side. This vessel, now and then, at irregular intervals, 

 dilates quickly and closes; the wave proceeding upward 

 toward the head, but only for a short distance, and 

 unattended with any impulse to the blood-globules. The 

 nature of this vessel, and its use in the economy of the 

 infant Crab, I can in no wise explain.* 



* For figures of these two forms the reader is referred to my Tenhy, 

 170, 172. 



