470 Holt — On the Eggs and Larvce of Teleosteans. 



The diameter varies from 1-07 to ri3mm. ; and there is a single colourless oil- 

 globule, -15— •21mm., occupying tte usual position at the uppermost pole. The 

 zona presents no features of special interest. The yolk is clear and homogeneous, 

 and the periritolline space is small. 



The embryo at this stage (fig. 18) has a short, free caudal region bent up over 

 the yolk. The otocysts (ot.) liave appeared as small round sacs, with a double 

 outline, in the usual position. The head and eyes are entirely unpigmented, but 

 a number of minute black pigment dots extend along the trunk on either side of 

 the notochord from the otocysts to the posterior extremity. 



A few larger black stellate chromatophores occur over the oil-globule. 



Development appears to be slow, and the species appears to be rather delicate. 

 None of these eggs hatched, and only one survived till the 29th June. 



The e^g then lay at the bottom of the vessel, a phenomenon which I have 

 frequently noticed in advanced ova reared in confinement in this laboratory {e.g. 

 ova of sprat, gurnard, &c.), and one wliich appears to be in no way attributable 

 to ill-health, as the larvfe emerge and are not appreciably less robust than their 

 fellows. That it is not due to a change in the specific gravity of the water is 

 proved by the fact that it occurs even in continually running water of the same 

 specific gravity. That moribund pelagic eggs should sink is easily intelligible, 

 but it is hard to understand why this should also happen to perfectly healthy 

 specimens. It is possibly brought about, in some instances, by the adherence to 

 the zona of particles of dust, &c., which find their way into the aquaria ; but 

 appears to be a regular feature of development in some species, e. g. T. vipera [cf. 

 Raffaele, oj). cit., p. 30). The embryo (fig. 25) now apjDears almost ready for 

 extrusion. The free caudal region is equal to the rest of the body. The eyes 

 are large, and the otocysts have increased in size, and are vertically elongated, 

 but as yet remote from the eyes. The pectorals (/>•/•) have appeared as small 

 semicircular folds in the usual position. The heart (/i.)is large, and beats actively. 

 The notochord (pi. xlix., fig. 25a) is stout, and its cells show a definite arrangement 

 into a dorsal and ventral series, the bases to some extent interdigitating, but never 

 approaching the cuneiform condition. The gut is large and perforate, and shows 

 two dilatations in the region of the pectoral fins. It is also slightly expanded near 

 the posterior extremity. The anus appears to lie just behind the yolk. The yolk 

 is still large, and nearly spherical, the oil-globule (o. g.) now occupying a jDosterior 

 position, in a well-marked periblastic pocket. A narrow marginal fin is visible in 

 the free caudal region of the trunk. The cephalic integument and the whole of the 

 surface of the yolk-sac {y. s.) is studded with minute tubercles, very conspicuous in 

 profile. 



I liave noticed a similar condition in individuals of several species {e. g. Calliony. 

 mus lyra, Clupea harengus, &c.). It is sometimes transitory, as in an earh' cottoid 



