494 ALLIS. [Vot. II. 
of the posterior prolongation of the supramaxillary furrow. The 
part below the furrow lies superficial to the angular element of 
the mandible, and is much larger than the other part which lies 
wholly in the dermis. In the 17-inch specimen there were 
sixteen pores in this group, thirteen of them in the lower por- 
tion of it; in the 20}-inch one, twenty-four, eighteen below the 
furrow ; and in the 27-inch one, sixty-four, with fifty-eight below 
the furrow. In the skull there were twenty-seven openings in 
the angular and supra-angular, corresponding to the lower por- 
tion of this group. 
Groups 12 to 17 extend from the lower end of the pre-opercu- 
lar fold almost to the lateral edge of the dermal bones of the 
top of the head. The pre-operculum lies just in front of the 
surface fold, and the pores of the different groups lie mostly in 
lines transverse to and extending on both sides of it. Some of 
them extend to the very edge of the fold, and others, at the 
upper end of the series, reach onto the surface of the upper 
postorbital. In this series of groups, in the 17-inch specimen 
there were one-hundred and fifty-two pores; in the 20}-inch 
one, one hundred and fifty-five; and in the 27-inch one, two 
hundred and five; while in the skull there were only eighty-four 
large and irregular openings, showing that the branches of the 
different systems lie mostly in the dermis. 
The total number of pores on one-half of the head of the 
17-inch specimen was seven hundred and sixty-two; of the 
201-inch one, seven hundred and twelve; and of the 27-inch 
one, eighteen hundred and thirty-one. Other adult specimens 
examined had intermediate numbers, showing that the pores 
continue to divide, the canals leading to them increasing corre- 
spondingly in number and extent, up to a late period, if not 
throughout life. 
il. , POSTLABVAL. FORMS. 
1. Primary Pores. 
As all the pores and branches of the peripheral canal-systems 
arise by the repeated dichotomous division of previously exist- 
ing pores and branches, it is evident that at some stage of 
growth each system must have been represented by a single 
