PLANKTON OF THE GULF OF MAINE 359 



It is not easy to reconstruct the life histories of planula? set free at the beginning 

 of the breeding season, which may be in May at Woods Hole or early in June north 

 of Cape Cod. It is possible that some of these pass through the scyphostoma stage, 

 that these produce ephyra?, and that the latter grow to sexual maturity — but proba- 

 bly not to a large size — that same autumn; for Hargitt (1902) found that in high 

 temperatures (19 to 20°, and upwards) the development of Cyanca mny go forward 

 so rapidly that the whole cycle, from planula to young medusa?, is sometimes com- 

 pressed into a period of 18 days. McMurrich's (1891) experience, however, that 

 planula? of Cyanea produced in May, which he kept under observation in the aqua- 

 rium at Woods Hole and apparently under favorable conditions, were still in the 

 scyphostoma stage at the end of August is sufficient evidence that the rate of larval 

 development is usually much slower than this even at summer temperatures. Nor 

 is it likely that if any great number of Cyaneas passed through two generations a 

 year at Woods Hole — that is, produced sexually mature medusa? in spring and again 

 in autumn — the fact would so long have escaped detection there, with marine col- 

 lecting carried on so intensively and continuously. It is also probable that in the 

 Gulf of Maine, with its cooler water, few of the larval Cyanea that are produced in 

 late spring and early summer (none of the late summer and early autumn crop) 

 attain the stage at which the young medusa? are set free ("strobila stage") before 

 autumnal cooling checks their further development. 



What few precocious medusa? may be produced in the gulf during some unusually 

 warm autumn or in some locality abnormally warm for its latitude probably perish 

 at the onset of winter without leaving issue. In short, the evidence is strong that 

 there is only one annual generation of Cyanea in the Gulf of Maine. Cyanea passes 

 the winter in the attached ("scyphostoma") stage until stimulated to renewed devel- 

 velopment by the rising temperatures of spring. 



Because of its life history, Cyanea is strictly neritic in its faunistic status. It 

 has generally been taken for granted that the American Cyanea, like Aurelia, passes 

 through the attached phase of its life history close to tide mark only, this being 

 the case in European waters where the larva? are described as attaching themselves 

 to stones, seaweeds, etc., along the strands where their parents are cast up by wind 

 and wave in the storms of autumn (Damas, 1909). So far as I can learn the scy- 

 phostoma stage of the American form of Cyanea has not been found at liberty in its 

 natural surroundings, but the fact that the newly liberated medusa? have often been 

 found in partially inclosed waters — e. g., Woods Hole Harbor — and the facility with 

 which the young can be roared from egg to medusa in the aquarium are sufficient 

 evidence that at least a large part of the stock of Cyanea inhabiting the Gulf of 

 Maine is produced in very shoal water. On the other hand, the presence of the 

 young medusas on Nantucket Shoals, where we saw many very small ones only one- 

 half to 1 inch in diameter floating by the Halcyon while tagging codfish on April 23, 

 1923, and over the western, northern, and eastern parts of Georges Bank, where spec- 

 imens 2 to 4 inches in diameter were plentiful on July 23, 1916 (stations 10347 and 

 10348), and August 13-20, 1926, proves that this medusa is equally able to pass 

 through its scyphostoma stage in depths of from 30 to 70 meters. 



