338 FISHES 



millimetre in diameter, that is about the size of many eggs which 

 develop in the sea; the follicles are ruptured before fertilisation 

 takes place, the embryos hatch, that is to say burst the egg- 

 membrane, about a month after fertilisation, but are retained 

 some time longer within the ovary, so that the whole time of 

 gestation is somewhat less than two months. Fertilisation 

 took place in the middle of September and earlier, hatching 

 from the middle of October onwards. The young are much 

 smaller and less advanced in development at the time of birth 

 than in the two families previously considered; in fact al- 

 though the fins have begun to develop, they are still " larvae " 

 similar to those of oviparous fishes soon after hatching. In 

 Sebastodes lazvis, the largest of the species of this genus, reach- 

 ing a weight of 30 lbs., Eigenmann estimates the number 

 of embryos in the ovaries at several thousands. 



The Comephoridae include only four species, three of which 

 live in deep water in Lakes Michigan, Ontario, and Lake 

 Baikal ; the fourth species is marine and occurs on the Pacific 

 coast of North America. Comephorus lives in the greatest 

 depths of Lake Baikal ; it is colourless but its eyes are very 

 large. It migrates to shallow water in order to give birth to 

 its young and appears to die after this process, numbers being 

 found dead near the shores of the lake. 



Of the four viviparous genera belonging to the Zoarcidae, 

 Zoarces viviparus is the only species whose gestation has been 

 carefully studied, and our knowledge even in the case of this 

 common fish is far from complete. Copulation has been ob- 

 served by one author at the end of March, while the present 

 writer found specimens with young ready for birth on the 

 shores of the Firth of Forth in February and March. It would 

 seem from this that the gestation lasts for a whole year, but it 

 is possible that the season of copulation lasts for a great part of 

 the summer and that birth may take place in some specimens 

 earlier than February. It is not known whether fertilisation 

 of the ova takes place immediately after the introduction of 

 spermatozoa into the ovary, or whether as in the Californian 

 surf-perches an interval elapses between the two events. The 

 eggs appear to be fertilised after they have escaped from the 

 follicles. Zoarces belongs to the group of shore fishes whose 

 eggs are rather large with much yolk and usually adhesive, 



