220 EVENINGS AT THE MICROSCOPE 



each or the smooth and glossy convexity comes into focus, 

 that is so peculiarly charming. 



Eeturning 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 dis- 

 tinctness, 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 be- 

 neath 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 colorless 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 pos- 

 terior 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 un- 

 attended 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 nowise explain. 



