OF PLANORBIS AT STEUSTHEIM. lOB 



I have endeavored in this memoir to explain these accelerations or skippings from which 

 the theory took its name, on pages 28, 29, 30, and the importance of this law in explaining 

 the partial or total obliteration of type characteristics in the embryos of some parasites, as 

 well as in the ordinary cases which occur in every group of animals. 



Herr Wiirtenberger deals with the Planulatus, Amaltheus, and Pettos groups, on all of 

 which I have published papers, and since he has quoted Waagen, who cites my work, and 

 since Herr Wiirtenberger also knew of my work on the " Embryology of the Cephalopods," 

 as is shown by his allusion to my name at the foot of page 35, it would be very interesting 

 to know how he escaped noticing that I had discovered and formulated the law which he 

 justly considers an important law of heredity, and to the exposition of which he had 

 devoted his book. 



In a note to page 35 he gives Branco the credit of having done in 1879 the work 

 which I had done in 1872 in my treatise on the Embryology of the Cephalopods, and 

 casually mentions that I had already done something of the same sort on the Goniatites, 

 a small sub-division of the Cephalopods. 



Here, unfortunately, he did one of his own countrymen an injustice, since this was one of 

 the parts of my work which was not original, it having been copied almost bodily out of 

 Gruido Sandberger's previous researches. I can, however, congratulate Herr Wiirtenberger 

 upon his recognition by full quotations of that much abused naturalist, Haeckel, who, not- 

 withstanding his great offences against the conservatism of reasoning in science, has given 

 a better analysis than any other living naturalist of the laws governing the relations of 

 animals to their surroundings and to each other. His critics, whose name is legion, do 

 him a monstrous injustice in allowing themselves to dwell wholly upon the errors and the 

 faults they can find, forgetting themselves, and blinding others to the substantial services 

 to science of this justly celebrated naturalist. My own indebtedness to him and to his 

 works is very great, as must be that of all those who strive to get some idea of funda- 

 mental laws. 



Though differing from him on essential points, still in his Generelle Morphologie der 

 Organismen he has given substantially the same view of the action of heredity in pre- 

 serving the type, and of the relations of growth to heredity and of heredity to the modi- 

 fications produced by the direct action of physical influences, as has been set forth in this 

 memoir. The differences lie principally in the estimate of the importance of the law of 

 natural selection, which he considers as of wider application than I think is at all justified 

 by any proofs which have so far been produced. 



APPENDIX II. 



On page 14, in paragraph next to the last, and again on page 31 in the first paragraph, 

 I allude to the general tendency to spiral mode of growth in all shells. 



I had in this memoir no opportunity to enlarge on this subject, and when the remarks 

 were written had not yet published any observations on this interesting subject. Since then, 

 however, in an evening lecture given before the American Association for the Advance- 

 ment of Science during the meeting of 1880, at Boston, I gave some account of the facts 

 as they stand throughout the MoUusca, and attempted to prove, so far as the absence of 

 experiment would permit, the hypothesis that the spiral forms of all shells, whether Ceph- 



