70 ON SOME LARVAL STAGES OF FISHES. 



division of each aperture into the two nostrils which exist on each 

 side in the adult takes place later. The convolution of the intestine, 

 although still simple, is much larger and more conspicuous in con- 

 sequence of the increase of the intestine in length. The heart has 

 the same relations as in the previous stage. The pectoral fin is 

 visible as a somewhat quadrangular membranous fold projecting 

 from the side of the body behind and below the auditory organ. 

 The great bluntness of the anterior edge of the head is very 

 characteristic of the larval sole at this stage. The mid-brain is 

 still very prominent dorsally. The dorsal edge of the primordial 

 fin still presents the two rounded projections described in the pre- 

 vious stage. The pigmentation of the skin is now more developed 

 than before. The length of the larva from which fig. 2 was pre- 

 pared was 4*2 mm., rather less than that of the specimen represented 

 in fig. 1. Fig. 2 represents the appearance of the larva as seen 

 partly by reflection, partly by transmission of the light ; the light 

 was partly excluded from the apei'ture of the stage of the microscope, 

 so that the specimen was seen against a somewhat dark background, 

 as shown in the figure. 



The stage shown in fig, 2 is the oldest which I have examined 

 in larvae reared in confinement from artificially fertilized ova ; all the 

 larvas I reared last year, died soon after this stage was reached. Fig. 3 

 shows the appearance during life of an older larva which I obtained 

 in Cawsand Bay, Plymouth Sound, on May 14th, 1890. It was 

 captured in a small trawl made of cheese-cloth and worked on a 

 sandy bottom in three to five fathoms of water. I think there can 

 be no doubt that this larva belonged to Solea vulgaris. I identify 

 it by the distribution of the pigment in the skin, especially the 

 spots on the dorsal and ventral fin, and by the shape of the head. 

 The tissues of the body, though still translucent, were no longer 

 transparent enough at this stage to show the internal organs so 

 clearly as at the stages previously described. The chief features 

 to notice at this stage are as follows. The notochord is bent up- 

 wards at its posterior extremity, and the caudal fin-rays are beginning 

 to appear beneath the bent portion. The lateral muscles of the 

 body are defined dorsally and ventrally by a distinct margin, 

 between which and the base of the median fin-membrane is a region 

 in which the interspiuous bones, is h., have begun to appear. The 

 liver, L, is visible as a large mass towards the anterior margin of the 

 abdominal cavity. Behind the intestine, int., is seen the urinary 

 bladder, ^l. h. The prominence of the mid-brain and the projections 

 of the outline of the longitudinal fin over the head have disappeared, 

 but the fin membrane still extends forwards in front of the eyes. 

 The eye has a blue colour, probably due to iridescence of the 



