﻿REPORT OF THE DIRECTOR ICjIO I97 



may be said to be congenital and so, without dispute, capable 

 of inheritance. A period of stress during group development 

 not only makes the factor of natural selection more effective but 

 it also adds to the number of avenues of escape tried by the 

 group, or in other words to more active variation and mutation. 

 Without stopping to quarrel over any Lamarckian factor let us 

 state this proposition in different terms. Evolutionary activity 

 in a group of organisms is always greatest during those long 

 periods of time when some particular antagonistic force or forces 

 bear more heavily on the group in question. Cambric or Pre- 

 cambric Pelmatozoa were under just such an increased environ- 

 mental hostility and their response was the massing and fusion 

 of mineral spicules into strong thecal plates. This very plate 

 formation, however, introduced new factors inimical to respira- 

 tion and led to exceedingly diversified and specialized types of 

 respiratory structures as early as the age of the Chazy beds or in 

 Ordovicic time. It is one purpose of this paper to point out 

 the mechanical effects of increasing mineralization and increas- 

 ing thecal regularity and show how these factors led to diversity 

 of structure. The subject will be approached largely from the 

 synthetic or deductive side. 



Primitive Pelmatozoa were creatures of the sea and respira- 

 tion could only be accomplished by appropriating oxygen which 

 the sea water had previously taken into solution. This oxygen 

 was largely passed through the epidermis (dermic epithelium) 

 and underlying membranes by osmosis, dissolved by the fluids of 

 various underlying cavities and so circulated through the body. 

 We may designate this as the epidermal supply and the epi- 

 dermis itself as the principal organ of primitive respiration. 



The entire supply could not have been epidermal for these 

 primitive forms swept water into their alimentary canals to- 

 gether with their food, and the amount of water used with the 

 food stream contributed to the oxygen supply. The endoderm 

 was thus made to assume a respiratory function. In later forms 

 water in still larger measure was admitted to a portion of the 

 enteric cavity, or at least to the proctodaeum through the anus. 

 Water entering any portion of the alimentary canal would have 

 its oxygen removed and would receive the products of com- 

 bustion in return. These alimentary tissues would then come 

 to function in a greater or less degree as respiratory tissues. 

 Such a system might well be distinguished as the alimentary or 

 enteric respiratory system. 



