224: THE OCEAN WORLD. 



higher animals: the common trunk canal is thus formed, which 

 directs itself to the stomach, receiving in its way thither all the 

 lateral "branches. 



A very distinct circulation exists in the Medusae. The peripheric 

 part of the stomach suffers the nourishing liquid which has heen 

 elaborated in the digestive cavity to pass : this fluid then circulates 

 through numerous canals, the existence of which have been clearly 

 traced. 



It is also a singular fact, that organs of sense seem to have heen 

 discovered in these Medusas, which early observers believed to be alto- 

 gether destitute of organization. " During my sojourn on the banks 

 of the Ked Sea," says Ehrenberg, in his work on the Medusa aurita, 

 " although I had many times examined the brownish bodies upon the 

 edge of the disk of the Medusae, it is only in the month past that I 

 have recognized their true nature and function. Each of these bodies 

 consists of a little yellow button, oval or cylindrical, fixed upon a thin 

 peduncle. The peduncle is attached to a vesicle, in which the micro- 

 scope reveals a glandular body, yellow when the light traverses it, but 

 white when the light is only reflected on it. From this body issue 

 two branches, which proceed towards the peduncle or base of the 

 brown body up to the button or head. I have found that each of 

 these small brown bodies presents a very distinct red point placed on 

 the dorsal face of the yellow head ; and when I compare this with my 

 other observations of similar red points in other animals, I find that 

 they greatly resemble the eyes of the Kotifera and Entomostraca. 

 The bifurcating body placed at the base of the brown spot appears to 

 be a nervous ganglion, and its branches may be regarded as optic 

 nerves. Each pedunculated eye presents upon its lower face a small 

 yellow sac, in which are found, in greater or smaller numbers, small 

 crystalline bodies clear as water." The presence of a red pigment in 

 very fine grains is an argument in favour of the existence of visual 

 organs in these zoophytes, for the small crystals disseminated in the 

 interior of the organ would no doubt perform the part of refracting 

 light which is produced by crystalline in the eyes of vetebrated 

 animals. Moreover, it is found that there are marginal corpuscles 

 analogous to these brown spots in other species of Medusae. They 

 are of a palish yellow, or quite colourless, and enclose sometimes a 

 single, sometimes many calcareous corpuscles. When they are colour- 



