of the Fishery Board for Scotland. 



299 



A comparison such as this, of ten cases, should be sufficient to show 

 that there is extreme irregularity in the arrangement of the various parts, 

 and the only case in which there is any approach to a bilateral symmetry 

 is that of Weber. Here the resemblance of the right and left organs was 

 complete, and both testes were apparently functional. The case cited 

 above as Howes, I., had the right ovary and testis closely resembling 

 in structure and mutual relationship the right organs of Weber's case ; 

 but, apart from these two cases, all the others appear to vary indefinitely, 

 although the female element usually predominates. The asymmetry 

 reaches a maximum in my second case described above and in the first 

 one described by Smith, in which there were three testes of varying 

 sizes, one median and attached * a little above the mouth of the ovisac or 

 ' oviduct/ another being 1 towards the left side of the opening of the ovisac 

 ' or oviduct, near its termination.' 



Weber, in the paper already referred to, gives a list of the various 

 species of Teleostean fish in which hermaphroditism occurs, and he classifies 

 all these according to the frequency of the phenomenon, so that they 

 form a series (commencing with forms like the cod, whiting, herring, etc., 

 in which this condition occurs only in an occasional specimen, and even 

 then with great irregularity, and culminating in the well-known 

 Serranus, which is normally hermaphrodite). 



There are obviously two theories which may be held regarding this 

 phenomenon, and the reason of its occurrence ; the more usual one is that 

 held by both Howes and Weber, namely, that which accounts for the 

 tendency to produce hermaphrodite individuals as due to atavism, the 

 cases being regarded as a reversion to an ancestral hermaphrodite 

 condition. 



There are numerous facts in the ontogeny and structure of the 

 Yertebrata which point to a hermaphrodite chordate ancestor. 



Amongst these we may cite Nansen's* observation of the protandric 

 hermaphrodite condition of the myxine and the important fact that 

 amongst Teleostei, as a rule, the males are considerably smaller than the 

 females, and there is in some cases (salmon, etc.) certain proof, and in 

 others a great probability, that the males are mature at a much earlier 

 date than the females. Above the fishes also, many of the Amniota show 

 a tendency for an earlier maturation of the male products. The bearing 

 of this may be seen as follows : — We may suppose the primitive herma- 

 phrodite chordate ancestor to have a continual rhythmical and perhaps 

 seasonal predominance of one sex more or less directly dependent upon 

 the environment (c/. Yung'sf observations upon Tadpoles). The 

 tendency for a seasonal repetition of the same environment would then 

 have the effect of causing a perfectly rhythmic sexual cycle, from male to 

 female, in each individual. This would be a case of polycyclic herma- 

 phroditism. (For this condition Howes used the terms 1 mw^'cylic,' and 

 ' unicyclic ' for monocylic !). 



This condition appears to be exemplified in the abnormally herma- 

 phrodite Teleostei. The lengthening of the cycles would result in a 

 monocyclic hermaphrodite condition, as still persistent in myxine, and 

 lastly, the reduction of the stage at the commencement of the cycle to 

 vanishing point in some individuals (females), and hypertrophy of the 

 former half in others (males), would eause a hemi-cyciic dioecious species, 

 as exemplified by all other vertebrata. If we may regard this as, in a 

 general way, the line upon which the dioecious condition has been 



* Aarsber. Bergens Mus., 1887, op. vii. 



t Arch. Zool. Expr., vii. Arch. Sci. Phys., Nat. xiv. 



