— 9 — JOHS. SCHMIDT 



difficulty in determining the postlarval stages of these 17 species from the external char- 

 acters alone (form, development of the (ins, pigment). It is only the two species Gadus 

 Esmarki and nihiiitits, which are often very difficult even impossible to be distinguished 

 from one another by means of the externa! cliaracters alone; but as will be shown in 

 discussing these two species in more detail, we possess a certain means of distinguishing 

 them in the number of vertebrae. These are easily counted after the small fish are dehyd- 

 rated and cleared in xylol or the like. Ehrenbadm especially has shown how great an 

 importance the counting of the vertebrae has for the identification of the young of lishes, 

 and I can fully confirm his judgment, with the addition that in future descriptions of the 

 young of species as yet unidentified the determinations should always be controlled by 

 means of the vertebrae.^ As mentioned, it is in the main only the young of G. minutus 

 and Esmarki in which the vertebrae require to be counted. The two specis G. virens and 

 pollachius are however often somewhat difficult to distinguish, though only at certain 

 stages, by means of the external characters; and it is therefore fortunate that here also 

 we possess in the number of vertebrae a sure means of distinguishing them, in the doubtful 

 cases that may arise. 



It is for the other species, as mentioned, possible to determine the postlarval stages 

 from the external characters alone, if that is to say the specimens are in any way fresh 

 and well-preserved, and this method is naturally the easiest in all cases. But if one has 

 to deal with old collections, where the pigment of the specimens is perhaps obliterated, 

 then the number of vertebrae is of excellent assistance, and I shall therefore in the follow- 

 ing descriptions of the species give the number of vertebrae for each one; these observations 

 on the vertebrae have been made in the course of years on board the "Thor" on a large 

 number of adult specimens of various gadoids. 



As the matter stands at present, we are able to determine the postlarval stages of all 

 the North Atlantic, shallow water species of gadoids (with exception perhaps of the genus 

 Onos), but we have only come so far within recent years. When the international investiga- 

 tions began in 1902—1903, the postlarval stages of but few species were sufficiently known 

 and distinguished from nearly allied species. In consequence of this it has only been 

 within recent years that a more systematic investigation could be made with regard to 

 the distribution of the postlarval stages of several species, after their developmental history 

 had become better known. -^ 



It would have been very desirable naturally, if not only the postlarval stages of the 

 17 gadoids species, but also their pelagic eggs could have been determined in our 

 samples and tabulated in the same manner as the fry. But in the present state of our 

 knowledge this has not been possible. 



1 It has only been in the course of the last two years that I have used the vertebrse on a large 

 scale to determine the postlarval gadoids, as I had previously believed that this could not be done fl'ith 

 the same ease as for the flat-fishes. Experience has shown however that with a little practice it is an 

 easy matter to count the vertebrœ in the postlarval round fishes. In order to fill up this gap in my 

 Gadtis monograph, I give the number of vertehrœ in, this work, as their number, especially of the 

 abdominal vertebrae, are excellently suited for diagnostic purposes within the genus Gadus. I use this 

 occasion to mention that I have subjected all the postlarval stages of the gadoids described and figured 

 by me to a renewed investigation in respect to the number of vertebrœ, and have thus in all cases had 

 further confirmation of the correctness of my determinations. 



^ This holds good for example for Gadus Esmarki, minutus, virens, pollachius, lusctis, Poutassou, 

 Gadiathis argenteus, Molva species, Merluccius etc. 



