Development o/ Qastrosteus spinachia. 495 



that of Teleosteans in general. The swim-bladder can be 

 made out immediately beneath the notochord ; but no anal or 

 urinogenital structures can be clearly distinguished. By the 

 twentieth day the heart has lost its simple tubular structure, 

 and, as a thin-walled sac, is flexed upon itself; and on 

 the twenty-first day the circulation is in vigorous action, a 

 great volume of corpuscles surging through the yelk-trunks. 



It is not proposed to make reference to the serial micro- 

 scopic sections of embryos which were prepared during 

 these observations, as space will not permit, and the prepara- 

 tions have not yet been completely worked out in the labora- 

 tory. It must suffice in this brief survey of the early stages 

 of Gastrosteus spinachia to note that the embryos emerge at 

 various dates from the twenty-fifth to the fortieth days after 

 fertilization — this variation in series of ova deposited at the 

 same date being due to their unequal rate of development, the 

 more central ova being longer, and the external ova being more 

 rapid in reaching maturity. The newly-hatched young are 

 soon richly supplied with pigment, bright yellow spots being- 

 scattered over the surface of the trunk, especially the dorsum, 

 and elaborate stellate black pigment-spots occurring on the 

 dorsal and lateral regions. They are very vigorous and 

 active, contrasting greatly with the frail embryos of our 

 common food-fishes, whose ova are pelagic. 



It may be noted that the temperature of the water in the 

 tanks during these observations varied from 41° F. in May 

 to 50° or 51° F. early in June. The unique situation of the 

 St. Andrews Marine Laboratory and its natural conditions 

 being unusually favourable for the development of the ova of 

 marine fishes, the phenomena observed in the progress of 

 Qastrosteus spinachia may be taken as almost normal. 



P.S. — It is remarkable that, whereas in the freshwater 

 sticklebacks the male during the breeding-season assumes 

 brilliant colours, the pectoral and ventral region being of a 

 bright scarlet tint, in the marine species no such distin- 

 guishing marks appear. Both sexes exhibit a similar marking. 

 The male alone appears to construct the nest, and though 

 female fishes, distended with eggs, often hover near during 

 the building process, none were observed at St. Andrews to 

 take any part in the work. The statement published by 

 Heincke * that the male and female fishes build the nest is 

 probably incorrect and due to the similarity of the hues of 

 both sexes. 



* ' lUustru-te Naturgeschichte d. Tliiere ' (Leipzig, 1882;, p. 400. 



