Medusce oj the Philippines and of Torres Straits. 167 



ing expression we might say that the medusae of temperate regions have 

 a larger " factor of safety" in respect to temperature. Harvey showed 

 that, upon heating, the rate of conduction of the nervous stimulus which 

 causes pulsation increases in an arithmetical ratio, so that its "curve" 

 is a straight line. At from 34 to 39, however, the curve makes a 

 sudden bend downward and the rate declines sharply. This decline 

 may be due to the effects of asphyxiation, for Winterstein showed that the 

 rate of oxygen consumption in jellyfishes is 3| times as rapid at 30 to 

 35 as it is at about 12 C. Thus the oxygen of the sea-water becomes 

 insufficient to support the augmented vital activities of the animal. 



The large, rich rosin-brown colored cyaneas of our New England 

 coast are not found in the tropics, but closely allied species reappear 

 in the south temperate zone, so that somehow they have managed, 

 perhaps in the glacial epoch, to cross the warm zone of the tropics. 

 Yet another set of forms, which are widely distributed over temperate 

 and warm seas, are creatures closely allied to the Dactylometra of the 

 southern shore of New England and southward, a jellyfish which may 

 be recognized by the reddish brown or purple radial streaks upon the 

 umbrella and its long, graceful, folded, curtain-like lips often beauti- 

 fully tinged with pink. 



We may distinguish five main divisions or orders of the larger 

 jellyfishes or scyphomedusae. 



I. The Carybdeidce or Cubomedusce, with bell almost rectangular and 

 with flexible tentacles mounted upon the ends of gelatinous wing- 

 shaped expansions. They have 4 knob-shaped sense-clubs, which are 

 very large and set within niches on the sides of the bell, with the eyes 

 all directed inward, apparently to command a view of the mouth. 

 These medusae have a marginal diaphragm which partially closes 

 the opening to the umbrella cavity. The Carybdeidae are confined to 

 tropical and warm seas and usually remain upon or near the bottom 

 until they become mature, when they often swim to the surface to 

 cast out their eggs and sperm. They are usually dull milky-yellow or 

 livid in color, and their tentacles sting so sharply that they are com- 

 monly called sea-wasps. None are known north of Cape Cod, but 

 they are well represented in the tropics throughout the world. 



II. The Stauromedusce are attached forms which do not pulsate. 

 The body is pear-shaped or pyramidal and the jellyfish fastens itself to 

 sea-weed or rocks by means of a stalk at the aboral end of the body. 

 There are usually 8 clusters of knobbed tentacles which are developed 

 at the pointed ends of 8 marginal lobes, and 8 large "anchors" or 

 sucker-like clubs upon the margin may alternate with the tentacles. 

 These forms are confined to cold seas and are known from the Arctic and 

 Antarctic Oceans, although they have never been found in the tropics. 



III. The Coronatce are usually deep-sea forms distinguished by their 

 peculiar dark purple or reddish-brown color, which is so characteristic 



