36 



EINAR LEA. 



[REP. OF THE "MICHAEL SARS" NORTH 



le sommet est dirige vers le haut. 1 ) Cet angle ne se 

 rencontre cependant que chez les jeunes exemplaires, et 

 il disparait peu a peu au cours de la croissance." 



In another place Zugmayer states that the number 

 of organs of the lateral line corresponds with the number 

 of vertebrae, and it occurred to me to ascertain whether 

 an analogous relation might be traced in our larva. I 

 found that at the sixth organ (one with 3 or 4 elements) the 

 lateral line bends sharply upwards, curving gradually until 

 it once more runs longitudinally, so I ran the risk of 

 removing the musculature from one side of the unique 

 specimen, and was able to ascertain that the vertebral 

 column, the elements of which were very slightly developed, 

 formed a strong curve upwards at the seventh or eight 

 myomere. When we consider that the anterior three 

 muscle-segments in a Leptocephalus correspond to the 



Fig. 35. Tail-tip of Gastrostomies Bairdii. 

 (After Zugmayer). 



anterior two vertebrae of the adult individual, 2 ) it is 

 evident that we have here a very striking feature common 

 to Gastrostomus Bairdii and our larva. 



Zugmayer (38) determined the number of vertebrae 

 in Gastrostomus Bairdii and found 110. I have had an 

 opportunity of removing the skin from one side of a 

 specimen in order to count the muscle-segments if possible, 

 and counted 107 with certainty, but the segments at the 

 very tip of the tail gradually became so indistinct that it 

 was impossible to be sure of the exact number. Gill 

 and Ryder (13) record 22 preanal and 75 postanal ver- 

 tebrae, or 97 in all, but they expressly state that the last 

 2 or 3 vertebrae were indistinct, so they give the number 

 97 with a query. The same difficulty arose with the 

 larva in question, but I was able to count 108 segments 

 32 or 33 being preanal, and there are probably not many 

 more. This approximate number of segments in the 

 larva, while not disproving its connection with Gastro- 

 stomus, is not very conclusive. But we find confirmation 

 in the structure of the tip of the tail with its peculiar 

 organ. Zugmayer (38) has given a drawing of the tip 

 of the tail, reproduced in fig. 35, and though not able 



to trace all the details in the figure, either in the larva 

 or in the adult animals I have examined, 3 ) I am satisfied 

 that the structure is practically identical. The long black 

 portion has the same shape, the caudal fin has the same 

 relative position, the segmentation in the lighter ventral 

 portion is present, but not quite so distinct and there is 

 even a faint indication of the peculiar papillae along the 

 dorsal margin. I am therefore in no doubt whatever 

 that the structure of the tip of the tail is another feature 

 common to Gastrostomus Bairdii and the larva in question. 



It may be mentioned that in this particular the larva 

 is distinguished from species A, which has also an organ 

 attached to the tip of the tail, but totally different in 

 structure. 4 ) 



On the whole therefore it seems reasonable to con- 

 clude that this larva is a young individual of the species 

 Gastrostomus Bairdii, and it represents a developmental 

 stage hitherto unknown. It adds a new link to the devel- 

 opmental history of this peculiar species, and enables us 

 by comparison with the previously known stages to sketch 

 the development of the species. 



The larva has the following dimensions: 



Total length 33 mm 



Anal 13-5 „ 



Dorsal 6-5 „ 



Height 7-2 „ 



Upper jaw 8-5 „ 



Lower jaw 7-5 „ 



Rostrobranchial distance 7-0 „ 



Branchioanal „ 7-0 „ 



We may add the following description: — 

 The trunk is compressed, but is stouter than that of 

 the ordinary Leptocephali. The segments visible through 

 the pigment are perpendicular to the vertebral column, and 

 the dorsal and ventral angles so common in leptocephalids 

 are absent. The lateral line runs, for the greater part, 

 intermediate between the dorsal and the ventral margin 

 of the body, but near the head it forms the curve already 

 mentioned (see pi. VI, fig. 5). The anus is situated far 

 forward, the anal fin being inserted directly behind it. 

 The dorsal fin is inserted not far from the head. The 

 anal fin and the dorsal fin have distinctly developed rays, 

 the number of which could not be determined. The number 

 in the anal fin exceeds 120, and in the dorsal fin 170. 



r ) The accompanying drawing shows that the fifth vertebra is bent upwards, so that the apex of the angle between the fifth and 

 sixth vertebra is directed upwards; in other words we may say that the anterior portion of the spinal column lies at a lower level than 

 the posterior portion, the fifth vertebra forming the connecting link between them. 



2 ) According to Grassi and Calandruccio (17). 



3 ) Only in one specimen could I see the small papillae to the number of ten, lying along the black portion. 



4 ) That the larva is distinct from species A is shown by other characters: thus in species A the foremost dorsal ray is situated very 

 much farther back than the foremost anal ray, whereas in the larva as well as in Gastrostomus the reverse is the case. 



