822 BIOPHYSICAL PHENOMENA [pt. iii 



In 1926 Sparta showed once more that most teleostean eggs have a 



rising specific gravity during development, but found that Gobius jozo 



was an exception, for the sp.g. of its eggs fell from 1-093 to 1-061. 



The course of the specific gravity has been charted out for a 



great variety of fishes by Remotti, some of whose curves are shown 



in Fig. 200. No satisfactory explanation of these phenomena has so far 



been given, but the experiments of PoHmanti are rather suggestive. He 



estimated the fatty acid content of various fishes, getting the following 



results: „ , , 



Table 94. 



^^ Fatty acids in % of 



dry weight 



Pilchard {Clupea pilchardus) 20-447 



Mullet (Mugil chelo) 12-609 



Anchovy {Engraulis encrasicholus) ... ... ... 9'i33 



Scorpion hsh (Scorpaena scrof a) ... ... ... 7-2 11 



Mediterranean eel {Congromuraena balearica) ... 6-768 



Blenny {Blennius gattorugine) ... ... ... 6-422 



Torpedo [Torpedo ocellata) ... ... ... ... 6- 100 



Sole [Solea ocellata) ... ... ... ... ... 5*448 



Dogfish (Scyllium canicula) ... ... ... ... 5'3i5 



Weever {Trachinus draco) ... ... ... ... 4'730 



Eel {Conger vulgaris)... ... ... ... ... 3'774 



Star-gazer (JJranoscopm scaber) ... ... ... 2-600 



Sole {Rhomboidjctis podas) ... ... ... ... 1-474 



Goby {Gobius paganellus) ... ... ... ... 1-115 



He then noted that this was also practically the order in which the 

 fishes would be arranged, beginning with surface and descending 

 to bottom fishes. He therefore suggested that the rise and fall of 

 fish eggs during their incubation period was probably correlated 

 directly with their changing content of fat. The influence of light 

 on these ontogenetic vertical migrations must also be considered; 

 indeed, according to Russell, it is the most important factor in them. 

 The eggs of fishes are not the only ones which move upwards and 

 downwards in this way. Similar migrations have been observed 

 in the cases of the chaetognath Krohnia hamata (Fowler), various 

 copepods (Farran and Kraeff't), the stomatopod Squilla (Santucci), 

 and the siphonophore Velella spirans (Woltereck). Zahony, who in- 

 vestigated the ontogenetic migrations of the chaetognath Sagitta 

 serratodentata, regarded temperature and not specific gravity as the 

 determining factor, but in support of Russell's view there are the 

 laboratory experiments of Groom & Loeb (on the acorn barnacle, 

 Balanus perforatus), and of Mast and Grave (on the tunicate 

 Amaroucium), who all noted a changing reaction to light during the 

 course of embryonic development. 



