5 6 4 



THE LOWEST ANIMALS. 



Pyrocystis (magnified 100 diameters). 



enable one to see the time by a watch, at a distance of a foot or more. A few- 

 organisms swimming or floating about in plenty of sea-room in a tumbler of water, 



will not become luminous unless the water be 

 shaken about, but when crowded together, they 

 become diffusely luminous, owing to mutual 

 jostling and irritation. The luminosity in an 

 individual sphere, which should be inspected with 

 a lens, may appear as a sudden, generally diffused 

 flash, followed by darkness or by less intense 

 light, or again, in the form of brilliant points of 

 light. The name of the organism, which belongs 

 to the flagellated infusorians, is Noctiluca. The 

 body forms a peach-shaped cyst, about one-fiftieth 

 of an inch in diameter, and with a tough mem- 

 branous wall. A groove on the surface sinks at 

 one end into a funnel leading into the interior. 



From the interior of the funnel there arises a large transversely striated flagellum, 



or proboscis, by means of which the animal swims, and there is also in the 



same place a fine whip-like flagellum. At the apex of 



the funnel there is a mass of sarcode, which extends 



itself as a wide-meshed, highly-vacuolated network, to 



the inner wall of the cyst, where it forms a thin layer, 



whence the phosphorescence emanates. Noctiluca 



multiplies by dividing into two, or by becoming 



encysted, after drawing in its flagella, and breaking 



up into numerous ciliated helmet-shaped " swarm- 

 spores." Frequently two organisms fuse into one w T hich 



may then divide up into spores. Noctiluca is found 



only in waters near land, the related forms met with 



in the open ocean belonging to the genus Pyrocystis. 



In one of the species of the latter the body is spherical, 



about one-thirtieth of an inch in diameter, and without 



the big flagellum. The phosphorescence, wdncli in each 



individual chiefly emanates from the nucleus, is dis- 

 played on the ocean surface on calm nights in the 



Tropics. Prof. Butschli regards this species as an 



encysted or resting phase of the common form- 



Noctiluca occasionally swarms in such abundance as to 



give in daytime a reddish or yellowish hue to the 



surface. When the sea is rough, the organisms are 



dashed below the surface, and do not form a sufficiently 



continuous layer to give rise to much luminosity, and 



when the wind is off shore they are blown out to sea. 



Among the Flagellata are included certain parasitic organisms, which, owing 



to their being immersed in nutrient fluids, are not compelled to seek further for 



food, and do not possess flagella. The Gregarina, living in the intestine of the 



MUSSEL-ANIMALCULE (S/l/?0>iychia 



mytilus) under surface. 



a, Mouth ; b, Contractile vacuole ; 

 c, Nucleus. (Magnified 150 

 diameters. ) 



