244 CtELENTERATES : ACALEPHS. 



common name, Jellyfish, was given on account of 

 their jellylike appearance and substance. 



If we examine the structures of Acalephs, we find a 

 cavity, which is the stomach, hollowed out of the mass 

 of the body, and this cavity has an opening which 

 serves as a mouth ; the edges of this opening are 

 turned outward and prolonged into delicate fringes. 

 And there are tubes which radiate from the center of 

 the body and unite \\ ith a tube at the circumference. 



The kinds of Jellyfishes are numerous, and they 

 var)' in size from those scarcely visible to those which 

 are one or two j'ards in diameter, and ■with tentacles 

 thirty or forty feet long ; and Mrs. Agassiz, in her 

 beautiful book, "Seaside Studies in Natural History," 

 mentions one which measured about seven feet in 

 diameter, and had tentacles more than a hundred feet 

 in length ! 



Jellyfishes are a hungry race, and feed upon their 

 own kind and other marine animals, which they 

 secure by means of their tentacles and lassos. On the 

 tentacles of Jellyfishes, and of Polyps too, there are 

 numerous lasso-cells, — too small to be seen without 

 the microscope, — each containing a long, spirally-coiled 

 thread or lasso, which can be instantly darted forth and 

 thrust into the little animal which is desired for food. 



Ctenophora. 



The Ctenophora are more or less spherical, or egg- 

 shaped, with eight ro^\'s of locomotive fringes dividing 

 the surface of the body, as the ribs divide the surface 

 of a melon. The Pleurobrachia is one of the most com- 

 mon kinds on the northeast coast of the United States, 



