20 EEPEODUCTION AND DEVELOPMENT OF TELEOSTEAN FISHES 



1*67 mm. in diameter, the difference being due partly to the 

 flattening caused by the pressure of the cover-glass, and partly 

 perhaps, to individual variation, as the eggs of a given species 

 always vary in size within certain limits. The position of the 

 groups of oil-globules at the sides of and beneath the embryo is 

 clearly shown in this figure. 



Historical and comparative. — Imperfect as is the foregoing 

 account of the ova of 8oIea vulgaris and their development, it is the 

 first definite information yet afforded concerning the eggs of this 

 species. Certain facts concerning the structure of the ova in the 

 genus Solea have been published by Dott. Fed. Raffaele in a paper 

 on the eggs and larvas of Teleostean fishes in the Gulf of Naples,* 

 which appeared in March, 1888 ; but Raffaele has only described 

 fertilized developing ova obtained by the tow-net from the surface 

 of the sea, and did not identify any of these ova with a definite 

 species. He ascertained the peculiarities of the ova in the genus 

 by examining mature ovaries of Solea itnpar, vulgaris, and Kleinii, 

 and says that these peculiarities, although distinguishing the ova of 

 Solea from any other pelagic ova, render the ova of the different 

 species so similar that they cannot, when obtained at random (i. e. 

 from the open sea) be distinguished easily from one another. 

 These peculiarities are those I have described, namely, the groups 

 of minute oil-globules, and the superficial layer of yolk-segments, 

 which Raffaele calls " vescicole vitelline," speaking of the whole 

 layer as the "zona esterna vescicolare." 



Raffaele describes two kinds of ova of Solea obtained by the tow- 

 net, and not having been able to determine their species, he calls 

 them Species A and Species B. Species A was 1'06 mm. in 

 diameter, and was obtained in January. He gives two figures of 

 this ovum, which are both indistinct, and also six figures of the 

 larva at different stages, which are much better. Species B was 

 larger, 1'23 mm. in diameter; of this he gives no figures of the 

 ovum, but three figui^es of the larva. Neither of these species 

 probably belonged to Solea vulgaris, as the largest of them is '2 mm. 

 smaller than the ovum of the latter according to my measurements. 



Raffaele notices the change in the relative position of tbe groups 

 of oil-globules as the blastoderm grows over the yolk, atti-ibuting it 

 to the fact that tbey are situated in the cortical protoplasm which 

 divides the vitelline segments, and therefore take part in the move- 

 ment of the latter. I cannot say whether the oil-globules in the 

 sole's ovum are freely movable at first like the single globule in 

 Scomber, Trigla, &c. 



* Le Uova gallegianti e le Larve dei Teleostei nel golfo di NapoU, Mittheilungen aus 

 der zoologischen Station zu Neapel, Bd. viii, Heft 1. 



