MEDts.K OF Woods HOLE REGION. 25 



waters of inland lakes. Must arc free swimming at sonic time during their life 

 history, yet not a few among both Hydromedusae and Scyphomedusae are per- 

 manently sedentary, sonic as degenerate sporosacs, others as polyp-like forms such 

 as the Lucernaridse. In distribution they range from a littoral to a pelagic life and 

 from the surface to abyssal depths. 



Under the head of Medusa? is also usually included a group of animals of similar 

 form and habits, though of somewhat doubtful structural affinities, namely, the 

 ctenophores or ''comb- jellies." While admitting a reasonable doubt as to their true 

 morphological relations, the ctenophores may still be most conveniently recognized 

 as a distinct class of medusa 1 and included within the present synopsis. Hence 

 species indigenous to this region will be noted and briefly described. 



Concerning the economic relations of medusa' very little is knov That they 

 sustain intimate general relations to the varied forms of marine lib m hardly be 

 doubted. Their vast numbers, wide distribution, and more or less i> ave life habits 

 all support the general inference. The well-known cases of commi alism existing 

 between medusa' and several species of fishes which follow them at Limes with more 

 or less persistence, often taking- refuge in the frills of the pendulous lobes of Scypho- 

 medusae, and resisting- efforts to separate them, still further suggest the probability. 

 Sonic fishes are said to feed upon the oral tentacles and margins, as well as the larger 

 tentacles of the umbrella, which they tear off at times with great vigor. Often, 

 however, the medusae reverse the operation and devour the fishes. It docs not seem 

 likely that medusa? can afford any large measure of food for fishes in general, but 

 several species of fish are known to feed upon them at times with great avidity. 

 The horned dog-fish, Squalus acantkias, when first arriving at Woods Hole in the 

 spring migration, in May, is said to feed largely on ctenophores. (H. M. Smith.) 

 The sun-fish, Mola inula, and also the tile-fish. Ahitera schoepjii, have been found by 

 .Mr. Vinal Edwards to have fed entirely on ctenophores and medusa'. 



As a special case of mutualism between tishes and medusae may lie mentioned that 

 of the young of the butter-fish, Rhombus triacanthus, found with Dactylometra 

 quinquecirra. Whether this particular case is of more than temporary nature may 

 be doubtful. So far as I am aware it is chiefly, if not wholly, limited to the period 

 of the young fish. Another case of similar character is that of the Portuguese man- 

 of-war. PhysaMa jjelagica, with its commensal, the Portuguese man-of-war fish, 

 Nbmeus grorwvii. In a single excursion in L894 the United States Fish Com- 

 mission collected 21 specimens of this fish, averaging 6 inches in length, all of which 

 were found associated with Physalia. A dozen specimens of Nbmeus have been 

 found under a single Physalia. (II. M. Smith.) 



While the importance of medusae as food for fishes may as yet be an open 

 question, there can be no doubt, on the other hand, that fish, especially the fry. are 

 an important article of food to many medusa'. Even small Hydromedusae, such 

 as Gonionemus, gorge themselves with fry frequently too large to be entirely 

 swallowed, and large medusa-, like Oyanea and Aurelia, arc often found with their 

 stomachs tilled with fish of considerable size, some of which are often in a partially 

 digested condition. It is not rare to observe the capture of minnows by medusa' 

 in the aquarium. In general, however, so far as my own observations go, the prin- 

 cipal food source of the smaller medusa' i> copepods, and since copepods also furnish 



