578 LÖNNBERG, OBSERVATIONS ON CERTAIN FLAT-FISHES. 



there are some peculiar exceptions, for instance, the ta i I seems 

 to be broader than in the parent-forms. N:o 1 is nearer the 

 turbot by reason of its large head and its great depth of body. 

 N:o 2 also has a large turbot-like head. The other ones al- 

 though interuiediate are a little nearer the brill in this respect 

 too. N:o 5 has got such a small head that it must almost be 

 regarded as anomalous in that respect. In regard to the deve- 

 lopment of the jaws all these hybrids (even N:o 1 and 2) are 

 nearer to the small-mouthed brill, hence we can note a definite 

 tendency in this matter. 



The measurement giving the distance between the ana! fin 

 and the tip of the snout in these five hybrids approaches that 

 of the brill more nearly than that of the turbot. 



With regard to the developraent or non-development of the 

 genital organs, these five hybrids off'er some facts of interest; for 

 the question whether they are fertile or not, is a natural and 

 inevitable one. N:o 1 is a male with well developed testidés. 

 N:o 2 is a female with a large ovary sac. Its posterior tip oii 

 the blind side lies 145 mm. from the genital opening, about 70 

 mm. of this length being situated in the secondary abdominal 

 cavity. Although so large the ovary seems empty and flabby 

 and it is very probable that this specimen has jusi Hnished 

 spawning. N:o o and N:o 4 have no visible trace of genital 

 organs or secondary abdominal cavity. N:o 5 is a male with 

 well developed testes. The two most essentially intermediate 

 forms are thus quite sterile. ^) Whether the two hybrid spe- 

 cimens, which most resemble the turbot and the one most 

 similar to the brill really are fertile can of course not be 

 quite definitely decided. It seems quite probable that they 

 produce eggs and sperm, hut the question is not thereby sol- 

 ved, for the raain thing is to find out whether these genital 

 elements are adapted for fertilization and developraent and 

 that cannot be ascertained without experiments. It is of in- 



^) This sterility can of uourse only be explained by hybridity and thus it 

 proves that hybridity is really present here. 



