60 H. W. MARETT TIMS. 
Mr. Stead (17), who throws considerable discredit upon the 
conclusions, and upon Dunker’s want of care in the establish- 
ment of his facts. 
Cunningham, in dealing with the ontogeny of the plaice 
(8), seems to imply that the cycloid precedes the ctenoid 
condition, but it is not evident upon what grounds he rests 
the implication. Holt has shown (9) that the scale tubercle 
of the adult turbot is developed from a simpler and more 
cycloid form in the young. It is, however, by no means 
certain that this scale tubercle is the homologue of the 
ctenoid spine, and not a special development. 
Wiedersheim (18) states that the cycloid scale is the more 
primitive, but without stating the grounds upon which the 
assertion is made. Hofer (7) is of the same opinion, basing 
his conclusion both on developmental history and on pale- 
ontology. With respect to the latter evidence this writer 
takes into consideration only the Physostomes of the Jurassic, 
whereas the earliest Teleostomes date back certainly to the 
Lower Devonian. The embryological evidence put forward by 
Hofer appears to me to be inconclusive, based on supposed 
histological homologies, and from the point of view taken in 
this paper is open to the objection that the scale and not the 
scalelet is taken as the morphological unit. 
Klaatsch (loc. cit.) claims a polyphyletic origin for the 
cycloid scale. It is beyond the limits of the present paper to 
enter into a general discussion as to all the ganoid, dipnoan, 
and other scales, but I may say in passing that such a 
complication appears to me to be unnecessary, and that the 
various scales, so far as I have knowledge of them, can be 
reduced to modifications of a single primitive placoid pattern. 
In consideration of the eminence of the authorities just 
quoted, one cannot but speak with the greatest difidence and 
regard this question as at least “non proven,” though as yet 
I have been unable to find any direct evidence against the 
view of the ctenoid ancestry for the cycloid scale. 
If the interpretation, that the individual scalelet and not 
the whole scale is the ultimate morphological unit be accepted, 
