120 



the testes are smaller than the ovaries, but still they are of considerable size, 

 and a considerable quantity of milt is produced. When we consider the small size of 

 the testes in the sole, and the small quantity of milt produced by a single male, it 

 seems difficult to understand how the large number of eggs produced by a single 

 female get fertilised at all. It seems to me that the only way to explain the facts is 

 to suppose that soles pair together like birds, or at least that the males do not like 

 some other fish shed their milt into the water at random, but shed it in the immediate 

 neitrhbourhood of a female at the moment when she discharges some ova. Some of 

 the wrasses pair and shed their milt in tliis way : I remember watching the process 

 once in one of the tanks of the Naples aquarium, but I do not remember to what 

 species the fish I saw belonged. 



After I had drawn the inference that some kind of direct fertilisation took place in 

 soles, I found my opiiiion supported in a curious way by a statement of Nordmaii in 

 his description of the fishes of the Black Sea, published in 1840 (see DemidofTs " Voy. 

 Euss. Merid. Zool., Ill, Poissons," Solea nasuta). The statement I refer to is that the 

 male and female of the species called by Nordman Solea nasuta, which is, as far as I 

 can see, the same as the Solea lascaris of the English coast, during copulation 

 adhere together by means of a glutinous liquid, and are sometimes taken in the nets 

 in this condition. 



The ripe ova pressed from female soles during the spawning period, when i)lac('d in 

 a bottle containing sea water taken from the surface of the sea at the place where the 

 fish are caught, float at the surface of this water. That ova so obtained are perfectly 

 ripe and uninjured by the artificial method by which they are taken from the fish is 

 proved by the fact that when milt is added to the water the eggs are fertilised, and 

 when taken on shore and kept in proper conditions will go on developing until they 

 hatch into normal young fisli. Tliis is tlie process of artificial fertilisation which will 

 be more fully considered in the next section. The observation of artificially fertilised 

 ova kept in aquaria shows the rate at which the development proceeds at a given 

 fenq:)orature, for it must be noted that the rate of development of all fishes' ova varies 

 considerably according to the temperature of the water in which they are contained. 

 The ft)llo\ving are the details of my observations on artificially fertilised ova kept in 

 aquaria : — 



May If), 1888. — Two or three soles' ova fertilised south of the Wolf Eock at 

 4 p.m. Temperature of surface of tlie sea, 50° F. (10° C). 



May 19. — One of the above ova still alive: the blastoderm had completely 

 enveloped the yolk, and the dorsal rudiment with Kupher's vesicle was 

 completely formed. Temperature in hatching jar, 5;^»'^0 F. (11"''7 C). 



March 23, 1889. — Several thousand soles' ova fertilised off" the Land's End promon- 

 tory at 7 a.m. Temperature of the sea water at surface, 48°'2 F. (t)°-0 C). 

 Eggs placed in hatching jar at the Laboratory the same evening. 



