NERVOUS SYSTEM OF JELLY-FISHES. 65 
nettles, sun-fish or Acalephs, of which there are about 
nine known species on the Eastern coast of the United 
States, we may study as the type of the suborder the 
common Aurelia flavidula Péron and Lesueur of our 
coast, which is closely allied to the Aurelia aurita of the 
European shores. It grows to the diameter of from eight 
to ten inches, becoming fully mature in August, the young 
appearing late in April in Massachusetts Bay, being then 
not quite an inch in diameter. The mature ones may be 
easily captured from a boat or from wharves. On a super- 
ficial examination, as well as by cutting the animal in halves 
and making several transverse sections with a knife, the lead- 
ing points in its structure may be ascertained. Its tough, 
jelly-like disk is moderately convex and evenly curved, while 
four thickoral lobesdepend from between the four large geni- 
tal pouches ; the oral lobes unite below, forming a square 
mouth-opening, the edge of which is minutely fringed to the 
end of the tentacles. On the fringed margin are eight eyes, 
each covered by a lobule and situated in a peduncle, and 
occupying as many slight indentations, dividing the disk 
into eight slightly marked lobes. The subdivisions of the 
water-vascular canals or tubes are very numerous and anas- 
tomose at the margin of the disk, one of them being in 
direct communication with each eye-peduncle. When in 
motion the disk contracts and expands rhythmically, on the 
average twelve or fifteen times a minute ; on the approach 
of danger they sink below the surface. 
While a distinct nervous system has not been discovered 
in Aurelia, Romanes suggests that there are primitive nervo- 
muscular cells, such as those shown by Kleinenberg to exist 
in Hydra, and he concludes, after a series of experiments 
on Aurelia aurita, that the whole contractile sheet of the 
bell presents not merely the protoplasmic qualities of ex- 
citability and contractility, but also the essentially nervous 
quality of conducting stimuli to a distance irrespective of 
the passage of a contractile wave. The later researches of 
O. and R. Hertwig show that the nervous system of 
Acalephe (Acraspedota or covered-eyed Meduse) is much 
more primitive than in the naked-eyed or craspedote forms, 
