ÖFVERSIGT AF K. VETENSK.-AKAD. FÖRHANDLINGAR 1894, N:0 10. 579 



terest however to remark that the specimens that approach 

 in their external characteristics iiearer to either of the parent- 

 forms than the others are more developed in regard to their 

 genital organs. — On the other hand it seems stränge that all 

 these interniediate forms, although intermediate, come a little 

 nearer to the physically weaker brill. The contrary might have 

 been expected, for hybrids are often more strongly developed in 

 their vegetative system; hut this is not the case here. These 

 are all rather small-raouthed and small-headed, — N:o 5 very 

 much so. That they however, have a good appetite is evident 

 from the fact that in the storaach of N:o 4 I found a Gadus 

 measuring. without head, 12 cm. and in N:o 2 a herring measur- 

 ing, without caudal, 12 cm. Some of these hybrids also had 

 Bothriocephalus punctatus in their intestine. This tapeworm is 

 a parasite belonging to Cottus scorpius, Lophius piscatorius, the 

 turbot etc; all of which are distinctly fishes of prey, but it is 

 not very often found in the brill. ^) Its presence in the intestines 

 of these hybrids shows thera to be rather voracious. 



Very much has been Avritten by various Authors ^) on the 

 forms intermediate between the plaioe and the flounder and 

 different opinions have been expressed on their nature as to 

 whether they are hybrids or only con verging varieties. I suppose 

 in reality both of these classes of forms exist. One specimen 

 the measurements of Avhich I have given (tab. 2) I suppose to be 

 a cross-species between the plaice and the flounder and I propose 

 here to give my reasons for this opinion. If it was a variety 

 only, it ought to be in all characteristics more similar to one 

 and the same species, even if some characteristics Avere inter- 

 mediate between those of the typical main-form and of some 

 related form, but no characteristics ought to come within the 

 limits of a second species. A hybrid, on the contrary, unites 

 characteristics from both parent-forms and has intermediate 

 characteristics as well. This form shows even in its external 



^) I have found it in one brill among seven. 



*) GoTTscHE, Nilsson, Möbius & Hkincke. Smitt a. o. 



