90 LOWER INVERTEBRATES. 



Probably all are marine and many genera gregarious, either seeking each otlier's 

 company, or huddled together by ocean currents or tide eddies. 



At spawning-time they are said to don brighter colors, or at least their ovaries and 

 spermaries at that time become more highly colored. Like the hydroids, their 

 organs for defence and offence are the stingiug-cells by which their bodies are covered. 

 Many sting with great violence, while others can be handled with impunity. None, 

 however, are destitute of stinging-cells. 



All are phosjshorescent, especially when irritated, while the color and intensity 

 of the emitted light varies with the genus. 



One of the most common Discophores in Xew England waters is called Ct/unea, and 

 is a representative of a family of moderate size known as the Cr.vxED.E. The most 

 sti-iking peculiarity of Ci/anea is its disk-shaped body, which varies in size from that 

 of a penny to several feet in diameter. Its color is reddish brown, but when dead and 

 waslied about for some time it becomes light blue. The body-disk is divided into two 

 well-marked regions, called the al)oral and the oral, or the ujjper and lower surfaces 

 as the animal naturally swims in the water. The upper surface is smooth and without 

 apj)endages, save little filaments which are remnants of bodies of considerable 

 size in the young of the animal. The under or oral surface is so called from the fact 

 that frotn it hangs not only the stomach with its mouth, but also many other important 

 structures. Tlie thickness of the disk in its centre is much greater than at the 

 periphery', where it becomes very thin and flexible, and capable of considerable motion. 

 Around the margin of the bell are found at regular intervals eight sense-bodies, which 

 lie in deep incisions in the rim. Each sense-body is a small sac or cyst mounted on a 

 sliort peduncle, and in the interior there are a number of rhombohedral otoliths of 

 calcareous composition. Each sense-body is covered by a thin, gelatinous wall stretched 

 above it, which is known as the "hood." From the existence of this hood in the 

 Discophora, and its absence in the Hydroidea, Siphonophora, and a few other jelly- 

 fishes, these animals are called the hooded-eyed medusae, while the latter are sometimes, 

 especially in older writings, designated the naked-ej^ed jelly-fishes. 



The most prominent of the several appendages which liang from the oral surface 

 of the disk is a thin, curtain-like body of great breadth, which is thrown into a great 

 number of folds and frills. This curtain is open below, and its inner walls make tjie 

 walls of the stonincli. It hangs far down below the oral surface of the bell, extending 

 far beyond it as the medusa, by strokes of the margin of tlie disk, is driven along 

 through the water. 



The tentacles of Cyanea arc found in bundles, in each of which there is a great 

 number of these organs. Each tentacle is long, thread-like, and \ery contractile, 



possessing stinging cells which, however, 

 are rather feeble in their action in the genus 

 Cijanea. The tentacles in larger specimens 

 of the genus reach an extraordinary length, 

 and, as in other Discophora, have for tluir 

 function the capture of the food. 



The genus Aitrelia, the type of the 



family Aureliid.e, is, next to Cyanea, one 



of the most common rc]iresentatives of 



the Discophora in New England waters. Although it never reaches the great size 



attained by the former, it may well be ranked as one of the largest of our Acalejjhs. 



