18 EEPRODUOTION AND DEVELOPMENT OF TELEOSTEAN FISHES 



ova of tlie whole number. The few I had were used up for micro- 

 scopic examination. 



In my next trip to Mount's Bay on April 3rd to 7th;, I took some 

 sole's ova as before, using entire testes cut into pieces to fertilize 

 the ova. But on my return I found that this time not a single ovum 

 was fertilized. At this time only a few soles were taken at a haul 

 on the Plymouth ground, and it was necessary to go to Mount's 

 Bay in order to have a chance of getting ripe specimens at all. But 

 after this nearly all the trawlers went round the Land's End and fished 

 on the north coast of Cornwall, so that it was difficult to arrange a 

 trip unless one was prepared to stay out a fortnight, which would 

 have made it impossible to get any results from the material obtained. 

 I sent the Laboratory fisherman on one of these loug trips, April 

 23rd to 28th, but the sole's ova he brought back were unfertilized. 

 He went again to Mount's Bay, May 8th to 13th, and was again 

 unsuccessful. I went myself May 15th to 18th, when I found a 

 good many of the female soles spent, but again failed to get milt ; 

 I employed the testes as before, and on my return on May 19th 

 I found a few of the ova fertilized. 



The common sole thus spawns in March, April, and May. The 

 temperatures of the open sea during the last two months are given 

 under Pleuronectes microcephalus. Off the Wolf Rock on March 6th 

 the temperatures were : surface 7*7° C, thirty fathoms 7"5° 0. I 

 found that sole's ova sank in water of r026 specific gravity and floated 

 at 1'027, so that their specific gravity is between these numbers. 



Structure and development. — The ovum of Solea vulgaris, after 

 extrusion and fertilization, is of considerable, size ; of two that I 

 measured one was 1'47 the other 1'51 mm. in diameter. It is dis- 

 tinguished from the greater number of the pelagic ova of other 

 genera by two peculiar characters, both connected with the yolk. 

 One is that instead of having a single large oil-globule, or a small 

 number of these, it has an immense number of very minute size. 

 These are arranged in groups of irregular shape, the globules of a 

 given group beiug all in contact with one another. At the early 

 stages most of these groups are near the edge of the blastoderm, 

 but without any constant arrangement (fig. 10) . The other character 

 is that the yolk is not perfectly continuous and homogeneous, but 

 co-extensive with the blastoderm there is a single superficial layer 

 of separate yolk-masses, or yolk-segments, having a somewhat 

 rounded outline, but not spherical {y. s. in figs. 10, 11, &c.) This 

 layer of yolk-segments extends with the blastoderm, so that when 

 the latter has enveloped the yolk the layer of yolk-segments also 

 envelops it completely, forming a superficial layer over the whole 

 surface of the yolk as seen in fig. XL When the embryonic rudiment 



