136 BULLETIN OF THE 
in the scleroblastic dermal cells to become osteoblasts, and in connection 
with this process it has developed a system of tubules for supplying 
them with nourishment. Moreover, instead of being formed simply as a 
continuation of the process by which the spine is produced, it has come 
to develop independently of the spine, for it is only in a late stage of its 
growth that the two become united. Thus the Ganoid scale plate seems 
to have arisen from the placoid basal plate by increase in size and with 
important modifications. 
2. The spine, on the other hand, has become reduced in size and in 
complexity of structure, and is in Ganoids (Lepidostens) only a rudi- 
mentary organ arising late and disappearing early, as is frequently the 
case with degenerate structures, the “wisdom teeth” of man being a 
familiar illustration of this. 
Hertwig’s view is that the scales of Lepidosteus have arisen by the 
fusion of numerous smaller basal plates of scales of the Selachian (pla- 
coid) type. Each spine upon a scale of Lepidosteus therefore represents 
a primitive placoid scale, and the whole Ganoid basal plate has arisen by 
the fusion of as many simple scales as the total number of spines formed 
upon its surface. Klaatsch objects to this interpretation, since the 
number of spines is so large and wholly indefinite, and because the 
spines lack such an orderly arrangement as that which the scales have 
in selachians. 
My own view in regard to this matter is essentially the same as_ that 
expressed by the latter author. Though the Ganoid scale must be 
regarded as a more highly developed basal plate than that found in the 
Selachians, its origin is not due to the fusion of many small ones, but 
rather to the calcification which in Selachians originated in connection 
with the formation of placoid spines, having become in Lepidosteus 
an independent process no longer dependent upon the impulse given by 
the growth of the spine. The hereditary tendency toward the growth 
and calcification of papilla still shows itself, however, in the formation 
of the small spines, though these are retarded in time and but feebly 
developed. 
As long as each spine had a basal plate, as in Selachians, the spatial 
requirement of this plate exercised a controlling influence upon the num- 
ber and the arrangement of the scales (= spines). When now, as in 
Lepidosteus, the spines have come to arise independently of the under- 
lying plate, such restraint is removed, and we consequently find an in- 
crease in the number of the spines and a lack of regularity in their 
arrangement. 
