94 Mr. R. Hitchcock on the 



complex shell as significant of a "7;/an so definite and obvious 

 as to exclude the notion of ' casuaV or ' aimless ' variation." 



The facts seem capable of a somewhat different interpreta- 

 tion, which seems more in accord with our present knowledge 

 of simple organisms, and quite sustaining the views of 

 Darwin that " plan," in the sense used by Dr. Carpenter, 

 should be superfluous. For if there be an inherent tendency 

 to variation among these organisms, as Dr. Carpenter seems 

 to believe, how do we explain the persistence of the original 

 Orbitoline type, 0. tejiuissima? Biologists seek to discover 

 the causes of variations which they observe ; but it seems not 

 less important that the persistence of types should also be 

 explained. 0. temiissima is a very ancient species, and 

 surely any inherent tendency to change would have mani- 

 fested itself during the long period of its existence, even under 

 unfavourable conditions. 



The observations I have to offer may be said to relate 

 entirely to change of environment ; but their tendency is to 

 demonstrate that the changes observed in the shells of this 

 family are not due to any inherent tendency resulting in a 

 definite plan, but that they are due to causes easily understood. 



It is far from my intention to deny a definite plan of growth 

 to these organisms. But plan of growth does not imply that 

 there have been causes acting within the organism — special 

 tendencies of the protoplasm toward higher structure. It 

 seems to be such an assumption that has led Dr. Carpenter to 

 speak of a "not understood" progressive tendency, &c. In 

 my opinion the causes of such progression as can be observed 

 are easily understood ; and the i)lan of growth becomes a 

 natural consequence of these causes, which are purely physio- 

 logical, and independent of any supposed tendency to varia- 

 tion. While Dr. Carpenter, on the one hand, seems to regard 

 variation as due to an inheient tendency of the protoplasmic 

 body, the writer, on the other hand, attributes it entirely to 

 the more or less favourable conditions of life of the different 

 species. Moreover, I am quite unable to understand how any 

 inherent tendency to variation impressed upon the sarcode 

 could fail to find expression in some differentiation of the 

 sarcode, which in the cases in question has not been ob- 

 served. 



The same view seems to be held by 0. Sclnnidt, wlio, in 

 his ' Grundziige einer Spongien-Fauna des Atlantischen 

 Gebietes,' alludes to Dr. Car})enter's previous studies, and 

 compares the changes observed in the Sponges and Forami- 

 nifera. lie says the changes in the latter are found in the 

 general habit of the form and the variable grouping of 



