42 



Treubia Vol. III. l. 



the increase of the number of trunk vertebrae, that of the post-anal ver- 

 tebrae decreases from more than 57 to 35. Thus we have to deal evidently 

 with a movement of the anus in the direction of the tail. The same was 

 observed in larvae of Conger mystax. In other species, however, as 

 e. g. in Muraena Helena, the situation of the anus proved to be much 

 more constant. In four larvae of this species, with a length of 9, 12, 

 1772 and 44V2 rnm, the number of prae-anal myotomes proved to be 

 constantly 80, a number reached in the Q.gg already. Truly, in an adult 

 specimen 70 prae-anal vertebrae only were counted. 



I am sorry I can not 

 p ^ find any information 



^ ~ — on this subject with 



regard to the herring- 

 like fishes. At my 

 request Dr. Redeke, 

 of Helder, has been 

 so kind to send me 

 a number of larvae of 

 the Zuidersea-herring. 

 As Dr. Redeke in- 

 forms me, Heincke in 

 his „Naturgeschichte 

 des Herings" (1898), 

 which I myself have 

 not at my disposal here, gives for the average number of caudal vertebrae 

 of this herring 13,9 (I.e. tab. 115). The total number of vertebrae being 

 about 55,5 for the Zuiderseaherring, we find for the trunk vertebrae 55,5 — 

 14 = 41,5 on an average. Now I found in 3 newly hatched larvae, one 

 with a yolk sack still and all measuring about 8 or 9 mm, 47 prae-anal 

 and ± 15 post-anal myotomes, and in an older larva, measuring nearly 

 20 mm, 45 trunk and ± 15 caudal myotomes. It is evident from these 

 observations and from what is found in the adult form, that in the Zuidersea- 

 herring the anus moves forwards during development. 



In newly hatched larvae o\ Chiro centras dorab I found 53—54 prae- 

 anal myotomes, and the same number in larvae of 48 hours, as represented 

 in fig. 4. 1 did not succeed in rearing them much further, but slightly older stages 

 were found in the catches. It appeared that in the next following stages a slight 

 increase of the number of trunk myotomes was to be noticed. In two slightly 

 older larvae, with the eyes still unpigmented and the yolk wholly used up, I 

 found 55, and in larvae of about the same length (6,8—7 mm), but with 

 black eyes (Figs. 7, 8), 57 — 58 myotomes in front of the anus. Then the 

 number begins to decrease gradually. In 3 larvae of 12^/4 mm I found 

 still 57, in one of 13^2 rn^i ^^i^ one of 18 mm each 56-57 myotomes 

 (it cannot be determined always with certainty, which myotome is to 



I _ — I 



im.M. 



Fig. 5, Head of a slightly older larva, with the yolk 

 nearly absorbed. The first gill-slit (*) has broken 

 through, the under jaw is growing out. 



