226 



THE AMKliK AX X . I TURALIST [Vol. LV 



lished in the San Juan Archipelago in 1904, it was found 

 that Melibe leonina was not uncommon in the vicinity, 

 although like many pelagic organisms its abundance was 

 subject to great fluctuations. In the summer of 1912 it 

 was particularly abundant, great numbers appearing 

 among the fronds of Nereocystis drifting past the float- 

 ing dock in front of the station. At this time Prof.H.L, 

 Osterud, of the University of Washington, gathered and 

 preserved a considerable number of specimens. The 

 largest specimen obtained was six cm. in length, the time 

 of collecting being the latter part of July. During the 

 season of 1913 very few were seen. In 1914, the writer 

 found several specimens of large size, 8 to 13 cm. in 

 length. These were taken among the floating eel-grass, 

 Zostera marina. In the summer of 1915 only two speci- 

 mens were found. It appears that the genus Tethys is 

 of spasmodic recurrence in the Mediterranean (Viguier, 

 1898). The appearance of Melibe does not seem to be 

 determined by any particular season, as Prof. Osterud 

 found specimens spawning when visiting the Biological 

 Station early in March of 1916. The period of existence 

 of this nudibranch must be more than one year, or one 

 season, judged from the sexual condition in this species 

 which has shown maturity in individuals ranging in size 

 from two to fourteen centimeters. Alder and Hancock 

 (1845), p. 24, think the period of existence for a large 

 number of species "not much exceeding one year." 



Ecology 



There is a striking similarity between the Klado- 

 hepatica\ not only between the nipm1)ers of any given 

 family, l.nt also hi'tween members of differont families 

 within the section. The former is wril illustrated by 

 T^'thi/s and J/r//7.r,meml)er>of the family Trthymelibiche. 

 This similarity is not <mly morpholo-ical, bnt e.|nally 

 true as to manner of li\ini;- and ^cm-ral hehaxior, for 

 instance, the method of swinnning. M. h'ni/in(i may 

 crawl on the leaves of the eel-grass; or it may float with 



