190 EVENINGS AT THE MICROSCOPE. 



well defined. It is the appearance of these facets, varying 

 according as the perfectly hexagonal outline of each, or 

 the smooth and glossy convexity, comes into focus, that 

 is so peculiarly charming. 



Returning now to the examination of one of the living 

 Zoeas, you perceive that the three pairs of pencilled limhs 

 do not represent any of the true legs; for the trans- 

 parency 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 pro- 

 jecting 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 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 no wise explain.* 



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

 170, 172. 



