558 DR. R. VON LENDENFELD ON THE SYSTEMATIC [DeC. 21, 



other leg of the cock grew as usual. This experiment I have 

 repeated several times in the same manner, with the same effects, 

 which led me to conceive that the spur of a cock would not grow 

 upon a hen, and that they were, therefore, to be considered as distinct 

 animals, having very distinct powers. In order to ascertain this, I 

 took the spurs of hen chickens and placed them on the legs of young 

 cocks. I found that those which took root grew nearly as fast, and 

 to as large a size as the natural spur on the other leg, which 

 appeared to be a contradiction to my other experiments. Upon 

 another examination of my hens, however, I found that the spurs had 

 grown considerably, although they had taken several years to do it ; 

 for I found that the same quantity of growth in the spur of a cock, 

 while on the cock, during one year, was as much as that of the cock's 

 spur on the hen in the course of three or four years, or as three 

 or four to one ; whereas the growth of the hen's spur on the cock 

 was to that of the proper spur of the hen as two to one." 



When a female animal belonging to a dimorphic species assumes 

 male characters, it is truly an example of Atavism, or development 

 of transmitted characters normally latent. 



This part of the matter has been dwelt upon at some length for 

 the following important reason. If we regard the epiblast and 

 the structures developed therefrom as representing the chief cha- 

 racters derived from the male parent, it opens up a field of interesting 

 inquiry in clinical medicine and pathology regarding hereditary 

 diseases, and it demonstrates clearly enough that wc have little 

 knowledge coucerning the germs of organs which may be latent in 

 an animal ; therefore Neogenetic Atavism is, at its best, exceedingly 

 questionable. To assume that such a form of Atavism exists, is to 

 believe in the sudden development of new characters : this is totally 

 opposed to the fundamental principles of Evolution. 



The question is one of great importance to the pathologist, 

 inasmuch as there is very great probability that many aberrations of 

 organs and tissues are atavistic in their nature. 



2. On the Systematic Position and Classification of Sponges. 

 By R. V. Lendenfeld, Ph.D., F.L.S., Assistant in the 

 Biological Laboratory of University College, London. 



[Received December 20, 1886.] 



I. Introductory Remarks, p. 558. 

 II. Nomenclature of Sijicules, p. 559. 



III. The Systematic Position of Sponges, p. 564. 



IV. The Classification of Sponges, p. 570. 



V. Key to the Recent Families of Sponges, p. 589. 

 "VI. Appendix. List of Publications, p. 692. 



I. Introductory Remarks. 

 Our knowledge of the development and structure of Sponges is of 

 such recent date that we have hardly had time to utilize it for 

 systematic purposes till now. 



