92 



Part III. — Sixteenth Annv.al Report 



The Ovaries. 



The anatomy ami structure of the ovaries of Teleostei have been de- 

 scribed by His,* Brock,+ Macleod,:|: and others. Such points in the minute 

 structure as bear upon my subject will be explained later when dealing 

 with the maturation of the ovarian eggs. It is, however, desirable here 

 to refer to some general features of the ovary in species which produce 

 pelagic eggs and in those whose eggs are demersal. If the ovaries of 

 either form be examined before the advent of spawning, they will be 

 found to be composed for the most part of relatively large, yolked, opaque 

 eggs, destined to be extruded in the approaching spawning season. 

 Among almost all forms with demersal eggs the difference in size, as well 

 as in appearance, between these large eggs and the small eggs which are 

 present in the ovary at the same time is very marked ; and further, the 

 large eggs approaching maturity are all of nearly equal size. For example, 

 in the lumpsucker {Cyclopterus lumpiis) the great mass of the eggs range 

 about 2 •2mm. in diameter, while the largest of the small eggs scattered 

 about in the stroma do not exceed 0'4mm. It is the same with many 

 other forms, such as the catfish, the herring, the smelt, the salmon, &c. ; 

 the two sizes of eggs being sharply demarcated from one another, and the 

 larger being subequal in size. This condition is associated with rapid 

 oviposition, the whole of the large eggs being extruded en masse, as 

 with the lumpsucker, or at brief intervals, as with the herring and the 

 smelt. In some other species with demersal eggs, such as the sticklebacks 

 {Gasterosfeus), the pipe-fishes {Sipignatlius), and the diminutive suckers 

 {Liparis)y three series of eggs may be observed, each marked off from the 

 other by difference in size, the two larger classes both containing yolk. 

 Thus in Liparis montagui, at the spawning season, mature eggs practically 

 of uniform size (1*1 to r2mm.; are present in the ovaries together with a 

 series ranging from about O'o to 0*7, and a third series of minute, clear, 

 yolkless eggs not exceeding 0'2mm. This condition is met with in small 

 species in which comparatively few eggs are deposited at one time, and 

 which shed their eggs in more than one batch or lot during the season. 

 The successive spawnings have been specially observed among the stickle- 

 backs. § 



In species which produce pelagic eggs there is not always the same 

 sharp demarcation between the large, yolked eggs, and those that are small 

 and transparent. Gradations in size may be detected between the two 

 groups, bat the degree in which this transition exists varies very much in 

 different species. In the larger forms, such as the cod, ling, plaice, tusk, 

 and turbot, there are comparatively few eggs of intermediate size, while in 

 the haddock, and especially in the whiting and gurnard, the intermediate 

 eggs are very numerous, and the gradation between the largest and the 

 smallest is readily perceived. This condition is associated with a prolonged 

 spawning period, and there is thus time for the smaller yolked eggs to 

 grow larger and to be expelled at the close of the spawning period. In the 

 larger forms, oviposition, although still prolonged over several weeks, owing 

 to the changes at maturation, is more rapid, the eggs shed in a given 

 season being all pretty equally developed when spawning begins. 



* Untersuch. iiber das Ei und die Eientwickelung bei Knochenfischen. Leipzig, 1873. 



t Beitrage z. Anat. und Histologic der Geschlechtsoi^ane der Knochenfische. Morph. 

 Jahrb. iv., p. 505. 1878. 



X Recherchea sur la structure et le developpement de I'Appareil reproducteur femelle 

 des Teleosteans. Arch, de Biologic, Tome ii., p. 497. 1881. 



§ Ransom. Observations on the Ovtuu of Osseous Fishes, Phil. Trans. Rov. Soc. 

 London, Vol. clvii., p. 431. 1868. 



