EGGS AND LARVAE OF TELEOSTEANS. 121 



that the large cells are situated beneath the periblast, and belong to the yolk ; 

 that they are not protoplasmic elements, but vitelline, although they have an 

 epibolic growth, and extend round the unsegmented yolk as this becomes 

 enclosed by the blastoderm and periblast. It is pointed out that the change in 

 relations of these superficial yolk segments shows that a transposition occurs in 

 the Teleostean ovum among the yolk elements closely analogous to the in- 

 vaginatory movement of the yolk in holoblastic ova. The diameter of the 

 ovum is "70 to 75 mm. The ova occur at Newport from the middle of June to 

 middle of August. At the yolk pole there is a single large oil globule. The 

 newly hatched larva is 2*15 mm. in diameter; the rectum is separated by a 

 distance of *275 mm. from the yolk sac; pigment is scanty; a series of black 

 chromatophores along the dorsal edge of the tail, and a few brownish-yellow 

 ones along the body and rectum. The structure of the notochord is not shown. 

 The development of the young fish was traced till a stage at which it measured 

 9 mm. in length. 



The presence of an oil globule, the externally segmented yolk, and the slight 

 separation of the rectum from the yolk sac, are the diagnostic features in 

 Temnodon, but how far these are characteristic of the family is not known. 



Fam. 3. Cyttid.e. 

 „ 4. Stromateid^e. 



This is a small family of marine fishes, containing only two genera. 

 Figures of Stromateus triacanthus, Peck, from a length of 7 mm. upwards, are 

 given by Agassiz in Young Stages, pt. iii. The notochord is apparently 

 multicolumnar, but no other embryonic or larval characters are to be discovered 

 from the figures. The species is called Butter-fish in America, and the young 

 at the length of 10-20 mm. are in the habit of sheltering themselves beneath 

 the umbrella of Dactylometra, one of the Scyphomedusae. 



Fam. 5. Corypilenid^e. 

 „ 6. Nomeid^e. 



,, 7. scombrid.e. 



According to Day, the eggs of Scomber scomber, the common mackerel, are 

 shed in May and June, and in the Brighton Aquarium have been observed to 

 be of the pelagic kind. The development of Cybium maculatum, the Spanish 

 mackerel, has been described by John A. Eyder (Bull. U.S. Fish Commission, 

 vol. i., 1881). The investigation was carried out in July 1880 at Mobjack Bay, 

 Virginia, and in 1881 at Cherrystone Harbour, Va. The eggs hatched twenty- 

 four hours after fertilisation, but the temperature to which they were exposed 

 is not stated. Evidence was obtained that spawning naturally takes place at 



VOL. XXXIII. PART I. Q 



