228 THE STICKLEBACK FAMILY. 



hatched the median fin is continuous and the head-region is 

 short and thick, elongating later to reach the adult proportions. 



The exact size on hatching has not been mentioned by Prof. 

 Prince, but when artificially extruded on the 5th June they 

 measured about 5 mm. in .spirit, and the yolk-sac was still large. 

 They are found in the rock-pools somewhat later (25th June) 

 measuring fths of an inch (about 10 mm.) with the larval tail 

 and are probably a week or two old. At 12mm. a considerable 

 portion of the larval marginal fin is still present — connecting 

 the tail with the dorsal, and extending in front of the latter. 

 The anal is connected in a similar way, and the pre-anal larval 

 fin is distinct. True rays are developed in all the fins (Plate 

 VIII, fig. 9). The larval tail is mainly distinguished by the 

 notochord, for it is slightly marked, only a faint incurvation in 

 the outline indicating it. Black pigment-specks cover the 

 entire body, and occur ventrally as well as dorsally. No spines 

 are yet present. Such examples are met with both in June and 

 July, the foregoing having been captured on the 23rd July. 

 At this date, others in the same pools are double the length, 

 showing that the period over which the spawning of the 

 various examples extends is considerable. At 19 mm. the adult 

 characters are more or less present, except that the body 

 generally is more slender, and the tail shows no trace of the 

 larval organ. In an example of this length small ova like those 

 of an ascaroid were present in the tail and in the dorsal fin. 

 Similar forms up to 26 mm. occur in July, some even reaching 

 this length on the 1st (in spirit). On the 6th August they 

 are found 47 mm. long. Later in the season they are found 

 in the harbour in October snapping at the small crustaceans 

 which abound in certain corners. They then measure about 

 65 mm. Growth is thus fairly rapid. 



In August specimens measuring 94 mm. occurred between 

 tide-marks in Guernsey, such being probably 13 or 14 months 

 old. In May a female of 135 mm. was probably 2 years old. 



Amongst the Elasmobranchii , or cartilaginous fishes, it has 

 been pointed out that the tendency for self-sacrifice for the sake 

 of the young is exemplified in a gradational manner by various 

 species, and it is especially important to notice that parental 



