THE DEVELOPMENT OP MOTELLA MUSTELA. 305 



Jtdis vulgaris (Hoffmann) : 52 hours. 



Scor]^(Bna porcus (Hoffmann) : 58 hours. 



Scorpcena scrofula (Hoffmann) : 58 hours. 



Merasfer acus (Hoffmann) : probably 58-60 hours. 



Spanish Macherel (Ryder) : 24 hours, some even 20 hours ; 

 and, if temperature unusually low, 36 hours. 



Codfish (Eyder) : 20 days (38° F.) ; has been known to hatch 

 in 13 days (45° F.). 



Codfish (Sars) : 16 days ; 18 days at very low temperature. 



Cunner {Otenolabrus c<srideus) (Kingsley and Conn) : 2 days. 



Merasfer acus (Emery) : 3rd day. 



Cunner and others (Agassiz and Whitman) : 50 hours. 



PsewdorhoQnbus ohlongios (Agassiz and Whitman) : 40 hours. 



Trachinus vipera (Brook) : 10th day, 58° E. 



Motella mustela (Brook) : 6th day, 55°-60° F. 



It will be noticed that the embryos in the above list hatch out 

 at a time varying from 20 hours to 20 days. The question isj 

 how far this disparity is a natural feature of the egg, and how 

 far it depends on temperature. I have already called attention 

 to the varying period at which the embryos of Trachinus hatch 

 out according to the temperature ; and there is no doubt that 

 within certain bounds a higher or lower temperature will propor- 

 tionately accelerate or retard the development of this species. 

 Unfortunately we have no details of the temperature at which 

 most of the observations were made. The species mentioned by 

 Hoffmann * were studied at Naples in the spring and summer, 

 when the temperature of the surface of the sea would be very 

 high, and thus far the short time taken to hatch out may in part 

 be accounted for. Ryder's observations f on the Spanish Mackerel 

 would also be carried on at a high temperature, but even taking 

 that into consideration, the development is remarkably rapid. 

 The same may be said of the observations of Kingsley and Couu^, 

 and Agassiz and Whitman §. The Codfish spawns in the winter 

 time ; and we notice at once the much greater time spent by the 

 embryo within the egg, and also that to some extent the date of 

 hatching depends on the temperature. In some of the non- 

 pelagic eggs laid in the winter, such as the Trout and Salmon, a 



* Natuurk. Verh. d. koninkl. Ak. Amsterdam, xxi. (1881). 



t Bull. U. S. Fish. Comm. i. (1881). 



t Mem. Bost. Soc. Nat. Hist. iii. (1883). 



§ Proc. Amer. Acad, of Arts and Sciences, xx. (1884). 



