SEA-URCHINS AND SEA-CUCUMBERS 



repetition of a single element. That element is a piece of 

 clear glassy material, highly refractive, of the shape of a 

 dumb-bell two globes united by a thick, short column. 

 The oval is constructed thus: suppose two dumb-bells to 

 be placed in contact, side by side, and soldered together, 

 there would be of course an oval aperture between their 

 columns. Then two other dumb-bells are united to these 

 in a similar manner, but one on each side, so that the 

 globes of each shall rest in the valley between the former 

 globes now united. These then are soldered fast in like 

 manner; and the result is that there are three oval aper- 

 tures. The next step is that on the top of the four united 

 globes two other dumb - bells 

 stand erect, and lean over 

 toward each other till their 

 upper globes come into con- 

 tact, their lower ones remain- 

 ing remote; these are soldered 

 to the mass and to each other, 

 at the points of contact, leav- 

 ing a fourth aperture. The same is repeated at the oppo- 

 site end by two other dumb-bells; and the structure is com- 

 plete as you see it. In almost all cases the two united 

 globes of these terminal elements are fused into one 

 globe, and in not a few instances the appearance is as if 

 these two dumb-bells were but one, bent over in a semi- 

 circular form; but still a good many specimens occur in 

 which the two dumb-bells can be quite distinguished from 

 each other. The calcareous matter that solders the ele- 

 ments together seems abundant, and has the appearance 

 that would be presented if they had been made of solid 



glass, and united by glass in a state of fusion; the latter 

 15 SCIENCE 15 



DUMB-BJCLLS IN HOLOTHURIA. 



