490 The American Naturalist. [May, 
sequence of the local aggregation in groups, due to local stimulation, 
of the underlying connective tissue cells. 
The Teleosts accordingly still bear traces of having a great capacity 
for developing the matrix of a protective dermal skeleton ; far greater 
than in other types. In birds, mammals, reptiles, and batrachia, of a cor- 
responding larval stage of development, the continuous cuticular or 
basement membrane beneath the epidermis, is either entirel - wanting, 
or is never developed except locally at relatively much later stages. 
There is also evidence to show that with the progress of evolution 
this primary superficial matrix has tended to be carried inward toward 
the cartilage so as to form the membrane bones, particularly on the 
head. Yet there are other regions where an engulfing of the superficial 
subepidermal calcifications in membrane occurs during the life of the 
individual. In the common sturgeon the preanal scales or scutes are 
The continuous investment of the mesoblastic tissue of the larve of 
recent scaleless Teleosts, such as Batrachus, by a structureless basement 
membrane which can be identified with a true scale matrix shows how 
persistently the armature of the Devonian types still tends to be inherited, 
even by a form not developing true scales, It is probably a good 
illustration of what Eimer means by his theory of ‘constitutional 
impregnation,” or, as one might say, saturation with inherited tenden- 
cies. 
With the advent of the body-cavity, gut-pouches, and mesoblast of 
triploblastic types, the mesogloea of the diploblastic type would be 
divided, that is to say, some of the matrix would be deposited upon 
the functionally inactive (in digestion) derivatives of the intestine, such 
sion, determined by purely physiological agencies, therefore gives both 
the matrix of the endoskeleton and that of the exoskeleton, The 
the intestine, that such a deposit can take place, 
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