438 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



In the general list of surface species only those that have been ac- 

 tually observed are introduced, but it must be remembered that the 

 greater part of the Crustacea, annelids, mollusks, and echinoderms are 

 well known to have free-swimming young, or larval forms, and that the 

 list might easily be doubled by the introduction of such species, on 

 theoretical grounds ; but, by omitting them, the list serves to indicate 

 how much yet remains to be done in this direction. There are large 

 numbers of common species of which neither the young nor the eggs 

 are known, and there are many others of which the eggs, or young, or 

 both, are known, but the time required for the hatching of the eggs and 

 the development of the young is not known. The dates given in the 

 lists refer only to the time of actual capture of the species, and it must 

 not be inferred that at other seasons of the year any of the species so 

 designated are not to be found ; for, doubtless, many of those that swim 

 free when adult may be found all the year round. And possibly 

 some species may breed during every month of the year. But the 

 breeding season of most species is probably of short duration, and 

 therefore the larvse and young may occur only at particular seasons. 



Mr. A. Agassiz has made a very large collection of the surface ani- 

 mals in Vineyard Sound, Buzzard's Bay, and off Newport, and to his 

 labors we owe the knowledge of a large proportion of the jelly-fishes. 

 He has also described the larvae and young of several Annelids and 

 Isemerteans, and has described and beautifully illustrated the larv?e 

 and young of the common star-fishes, (Asterias.) and the green sea- 

 urchin, {Strongylocentrotus DrohacMensis.) The Salpa Cahotti (Plate 

 XXXIIT, figs. 254, 255) was also well described and illustrated by him j 

 and also other species, but a large part of the collection has not yet 

 been elaborated. 



Our surface collections were made both in the day and evening, 

 at various hours, chiefly by means of towiug-nets and hand-nets. The 

 evening or night hours are generally more productive than the day-time 

 in this kind of collecting, but we were unable, owing to lack of time 

 and superabundance of other specimens, to do as much night-collecting 

 as we desired. 



Among the Crustacea there are a considerable number of species that 

 swim at the surface when adult, and others till nearly half-grown, but 

 the majority are free-swimmers only when quite young, or even only 

 when in the zoea and megalops stages, through which they seem, from 

 Mr. S. I. Smith's observations on several of our species, to pass in a 

 short time. TLie males of the common oyster-crab, rhinotlieres oslrcnm, 

 (p. 3G7, Plate I, fig. 2,) were often caught in the day-time swimming at 

 the surface in the middle of Vineyard Sound. Tiie huly-crab, natyon- 

 ichus ocellatus^ (p. 338,) of full size, was also occasionally caught swim- 

 ming actively at the surface. The " blue-crab,'' or common edible 

 crab, Callmectes hastatus, is well known to be an active swimmer, when 

 adult, but most of those seen at the surface were young. The larva' 



