DelsmaN: Fish Eggs and Larvae. 41 



in the reverse direction. Only in the anterior myotomes, close behind 

 the ear vesicle, can this crossed arrangement not be noticed. 



In all these respects, then, our larva agrees with those of the Clupea- 

 species and related forms, of which I have reared a fairly large number from the 

 eggs. For further determination we will have to take into consideration the 

 number of myotomes. The total number gives slight indication only. The fore- 

 most myotome, close behind the auditory vesicle, can easily be made out, not 

 so, however, the hindmost. In the tail the myotomes become gradually smaller 

 and smaller, finally to pass into the undifferentiated tail knob. Though often 

 it may be possible still to determine the hindmost myotome, yet we are 

 not sure that during the development of the larva no new ones are added. 



From this it appears advisable to direct our attention first to the 

 praeanal or trunk myotomes. What relation is there between their number 

 and the number of trunk vertebrae in the adult fish? I could find only very 

 little on this subject in the literature at hand. It is much to be regretted that 

 Ehrenbaum, in the numerous figures of his "Nordisches Plankton, Eier und 

 Larven von Fischen", nowhere indicates accurately the number of myotomes, 

 hardly ever does he mention it in fact. Perhaps a more thorough examination 

 of the literature than was possible to me would reveal some more obser- 

 vations on the subject, but the literature at my disposal is far from complete. 

 Moreover my impression is that the majority of the authors have not paid 

 much attention to the number of myotomes. In general a vertebra originates at 

 the limit of two myotomes, but is has not yet been ascertained for Teleosteans, 

 as far as I know, what occurs in the occipital region of the skull and how many 

 vertebrae are incorporated into the latter. I feel sure, however, that the number 

 of myotomes corresponding to vertebrae which are incorporated into the 

 skull cannot be great, for in the larvae I always found only three myotomes 

 on each side in front of the rudiment of the shoulder girdle, and only of 

 the two vertebrae forming between these could it be imagined that they 

 might be incorporated into the skull, although this is not certain either. 



A second question is, whether the situation of the anus may be 

 considered as fixed or whether a certain displacement of the latter in forward 

 or backward direction is possible. In rearing my larvae I have often got 

 the impression that the situation was fixed. In Fistularia, e. g., with its 

 large number of myotomes, I found the anus in succeeding stages always 

 under the 50th myotome. 



However, as follows from SCHMlDT's observations ') on eel-larvae, 

 this can not be relied upon. He found especially in species of Conger 

 during the development a strong increase of the number of the prae-anal 

 myotomes. In Conger vulgaris e. g. this number was 89 in a larva of Q mm, 

 100 in one of 12,5 mm. and 125 in one of 74 mm. In still older larvae, 

 up to 130 mm, it showed a slight decrease, to 121. Simultaneously with 



') J. Schmidt, 1913, On the identification of Muraenoid Larvae in their early ("prelepto- 

 cephaiic") stages, in: Meddelelser fra Kommissionen for Havundersögelser, FiskeriBd.IV.2, 



