SECT. m. CILIOGRADE HYDROZOA. 101 



boundless meadow in the yellow leaf. He was five or 

 six days in sailing through, them, and in about sixty 

 days afterwards, on returning from England, he fell in 

 with the same school, as the sailors call it, off the 

 Western Islands, and was three or four days in sailing 

 through them again. Mr. Piazzi Smyth, when on a 

 voyage to Teneriffe in 1856, fell in with a vast shoal 

 of medusse. With a microscope he found part of the 

 stomach of one of these creatures so fall of diatoms of 

 various forms stars, crosses, semicircles, embossed 

 circles and spirals that he computed the whole stomach 

 could not have contained less than 700,000. The flinty 

 shells of the diatoms ejected in myriads by the medusae, 

 accumulate in the course of ages into siliceous strata, 

 which, heaved up by subterranean fires, at length be- 

 come the abode of man. Thus gelatinous transparent 

 beings indirectly aid in forming the solid crust of the 

 earth by means of the microscopic vegetation of the sea. 



Ciliograde Hydrozoa. 



The ciliograde Acalephse, which form four orders and 

 many genera, and which swim by means of symmetrical 

 rows of long cilia, are represented on the British coasts 

 by the Cydippe pileus and the Beroe Forskalia (fig. 116), 

 little delicately tinted, gelatinous, and transparent ani- 

 mals that shine in the dark. 



The Cydippe pileus is a globe three-eighths of an inch 

 in diameter, like the purest crystal, with eight bands of 

 large cilia, stretching at regular distances from pole to 

 pole. A mouth, surrounded by extremely sensitive ten- 

 tacles, is situated at one pole, the vent at the other. The 

 Cydippes poise and fix themselves to objects by means of 

 two very long tentacles, fringed on one edge by cirri, 

 that is, short curled tentacles. These cirrated tentacles, 

 which in some species stretch out to more than twenty 



