20 



centini. in lengtli. invariably of an almost black line, and is accoiiipanieil by one or more dai-k bands on the head, running 

 parallel to one another (PI. HI, fig. 1). This neck-band runs straight down in front of the eyes, forming a curve over the back of 

 the head with the concavity to the front (in the 110 millini. long foetus, it forms an anteriorly open angle). In front of 

 this blue-black band, the general colour of the iiead is lighter. The region surrounding the nasal aperture is light, while 

 again, that lying a little in front of it is darker, the anterior boundary of' the dark colour being a little above the snout 

 portion (Fig. 2). There is, however, a diffuse colouring along the median line, which spreads to the front and includes the 

 apex of the upper jaw, wliicli is somewiiat darker. Three zones, in all. are distinguishable on the head. The colour of the 

 head in the smaller f(etuses is more like a thin shade, while in the larger ones (e. g. 170 millim.) it is darker, and advances 

 from the side towards the middle. In this way the present species (L. acutus) exhibits at a certain stage a colourless part 

 over the snout, which recalls L. albirostris. Towards the back the dark colouring passes into a continuous whole, so that 

 the hack anil upper part of the sides are dark, the intensity of the colour diminishing posteriorly. The darkest part is that 

 near the "neck-band" and round the eyes, while the eye region itself is colourless (fig. 2). On the lower eyelid, however, 

 just below the eye fissure, a dark spot is visible, which increases in size with the growth of the embryo. From the lower 

 part of the dark ring surroiniding the eye, a more thinly coloured band stretches backwards to the pectoral fin, (Fig. 2), 

 which exhibits a widely-spread, lighter colouring on its outer side. The part round the dorsal fin is lighter, while the lower 

 part of the fin itself is a little darker, the point again being light. A narrow dark line runs behind the dorsal fin along the 

 median line, while the adjacent regions are lighter. On the side surfaces the dark colour spreads right back to the tail and 

 the t.iil-lobes. at first only as a faint tinge, l)ut becoming more pronounced as the embryo increases in length. The dark 

 shade of colour on the sides spreads down until it is on a level with the eye, and, behind the navel, still lower. There is, 

 however, on the 170 millim. long fu'tus. an oblong patch of white on each side of the hind part of j the body, namely, that 

 part extending backwards from the frontal plane through the navel. — a "dorso-lateral'' band, recalling the light band-like 

 patch characteristic of the Lagenorhynchus acutus. There is also, in the somewhat older foetuses, an oval colourless region 

 situated above the pectorals. 



The tail-lobes, on both their upper and under surfaces, have begun to acquire a light grey tinge. 



The surface of the abdomen is without colouring until beyond the anus, although a tinge of grey is discernible 

 on the ])reputium penis. 



On a microscopical examination of skin sections, the pigment granules are found deposited in the region around 

 the nucleus. 



VI. ^^'hen the fætus has attained to half its full size. i. e. from 40 to 50 centim. in length, most of the 

 external si)ecific characters have already made their appearance. A 455 millim. long fætus, which' was at our disposal, 

 had, it is true, a somewhat defective epidermis, but nevertheless possessed characteristic marks. 



The fætal flexion of the facial region of the head is still apparent, but only slightly marked; the arched forehead 

 and cranium, and the roimded snout show the fo-tal character. 



The dolphin's "beak" is very much developed, but still round and stumpy. Six fætal hairs may be counted on the 

 upper lip. The nasal orifice is a transverse fissure with full lips, lying a little in front of the frontal plane of the eye. The 

 head is 'A of the length of the body. The pectorals (71 millim. long) amount to '/,;.4 of the length of the body. The insertion of the 

 umbilical curd lies in front of the middle of the body, and directly below the dorsal fin. This fin, which is 58 millim. high, amounts 

 to nearly '/ij of the length of the body. The postanal portion is very much compressed and high. It forms, anteriorly to the beginning 

 of the tail-lobes, a narrow ridge, which sinks into a low keel on the upper and under surfaces of the tail-fin itself. This fin, 102 millim. 

 broad (about V.i of the length of the body), has a deep groove in the middle, and is cut out behind in the shape peculiar to the genus. 



The extent of the very dark colour was somewhat difficult to determine in the specimen examined, on account of 

 its defective epidermis. It can, however, be stated that almost the entire head is of an even blue-black colour, while the 

 beid< is light grey. The region round the eye has also become black, as also the entire pectorals, with the exception of the 

 lighter grey streak from the eye to the axilla. The darker colour on the sides has spread farther down than before, while 

 the peculiar side patch is more limited. The dark colour on the tail has spread right down to the under side, and ceases 

 a little behind the anus. 



VII. Under the headings "almost full-grown'" and "full-grown", I have classed foetuses of from 75 to 95 centim. 

 in length. Four such were examined, of whith one 745 millim. one 825 millim.. and one 842 millim. in length, are considered 

 as "almost full-grown'", and one 950 millim. long, as a "full-grown" fætus. The 842 millim. long tætus is depicted 

 in Fig. 1 in the letter-pres. 



According to the geiu'ial rule, the size of a new-born Toothed Whale should be \.-! of the mother's length. As 

 the male in this species is bigger than the female, and their greatest length, according to Rasch (66) is 2.630 male, and 



