47Q 



TEXT-BOOK OF ZOOLOGY 



the species selected for description is of common occurrence on the 

 European coasts, where in late summer and autumn it frequently makes 

 its appearance in countless numbers. 



B. Constitution of Body and Colour. 



When thrown on shore by a boisterous wave, the soft body of one of 

 these animals, which is saturated with water, soon disappears. The open 

 sea is. indeed the element of these delicate, transparent creatures (see 

 fresh-water polyp). In its waters they swim about gracefully, exhibiting 

 light blue and red tints, and, to all appearance, in perfect peace. 

 Anyone, however, who has ever encountered them while bathing 



Longitudinal Section through an Aciiaspedote Medusa (Diagrammatic). 



a.S., External and, i.S., internal cutaneous layers (ectoderm and endoderm) ; St., supporting 

 or jelly layer (mesoderm); M., mouth; H., body cavity: r.K., radial canal, running to 

 edge of umbrella ; E., ovary ; F., gastric filament, projecting into the body cavities ; 

 Ah. , recesses (genital chambers) on lower surface of umbrella ; L. , a lobe of the umbrella, 

 covering E. , a marginal sense body, or tentaculocyst. 



knows that they do not bear a bad reputation entirely without reason, 

 though their stinging powers are but slight. 



C. Structure. 



Though the jelly-fish has externally only a slight resemblance to the 

 fresh-water polyp, a closer inspection reveals a complete similarity in 

 their plan of structure. This is at once shown by a comparison of the 

 appended illustration with that shown on p. 468. Let us imagine the 

 body of a fresh-water polyp flattened out into a disc, and the supporting 

 layer in the lower part of the body thickened into a broad gelatinous or 

 jelly layer ; let us further imagine the lower surface of the disc recurved 

 inwardly, so that its central portion hangs downwards like the handle 

 of an umbrella ; and finally let us picture to ourselves this handle, at the 

 end of which the mouth is placed, drawn out into four fringed lobes or 

 processes, and we shall have a fair representation of our jelly-fish. To 



