Mr. R. Hitchcock on the Causes of Variation. 93 



fact that of the six female specimens now before me two have 

 twenty, while the others have only nineteen annuli ; in other 

 Avords, the result to which I was led {torn. cit. p. 176), a good 

 deal to ray surprise, as to the great value of the number of 

 rings in the body, is a little shaken, although it falls in rather 

 with one's general experience as to the specific value of num- 

 bers such as these. It is to be noted, further, that the two 

 females with twenty annuli measured respectively 75 and 

 80 millim., or less than three with nineteen rings, which 

 measured 90, 95, and 105 millim. ; a specimen of 46 millim. 

 in length had nineteen rings. 



The fact that the male has seventeen annuli, while that of 

 P. protelis has sixteen or seventeen, and the discovery of the 

 fact that the female of P. poJyzonum is not absolutely limited 

 to nineteen rings, diminishes the gap that separated the two 

 species, Mr. Iloyle being apparently inclined to give as much 

 importance as I did to the seeming constancy of the number 

 of rings in the female. 



While these considerations, then, tend to the union of the 

 species P, protelis with P. 2)oltjzonum, the fact that Iho two 

 animals, the small carnivore and the voracious snake, do 

 live in the same area gives a clenching force which, to my 

 mind, is almost irresistible. 



XII. — The Causes of Variation. By ROMYN HiTCHCOCK*. 



The recent studies of Dr. W. B. Carpenter upon Orhitolites^ 

 are of special interest, owing to the remarkable manner in 

 which the stages of variation and development have been 

 traced. The monograph by Dr. Carpenter, published in the 

 Reports of tlie ' Challenger ' Expedition, was the subject 

 of some remarks recently made by the writer before the 

 Biological Society of Washington, in which an effort was 

 made to explain how such a simple sarcode organism as the 

 animal Orhitolites has been led to produce a shell of complex 

 form. Dr. Carpenter regards it as the expression of a ]iot 

 understood " progressive tendency along a definite line towards 

 a higher specialized type of stnicture in the calcareous fabric." 

 This, however, is merely a statement of the facts observed, 

 and in no wise assists in their explanation. Elsewhere it 

 may be gathered from the author's words that he regards the 



* From the * American Journal of Science ' for July 1884, pp. 49-52. 

 t Phil. Trans, part ii. (1883). 



Ann. & Mag. N. Hist. Ser. 5. Vol. xiv. 8 



