1919^ On Some Generic Distinctions in Sponges 19 



is at bottom discontinuous, in other words, that quantitative differ- 

 ences are to be looked on as summations of minute unit differences. 



That the Mendelian gene, whether or no it have a material, discrete 

 body and a location in the germ substance, may be thought of some- 

 what in this way, has been pointed out by several, H. S. Jennings- 

 and F, B. Sumner'^ among others. Sumner's facts and thinking, in 

 the paper referred to, are of especial interest to zoologists dealing 

 with the classification of natural races, who would like to knit up 

 systematics more closely with the study of variation and heredity. 

 A quotation shows how close my own standpoint is to his in respect 

 to certain points. In speaking of some mouse races, he sums up : 

 "It is quite plain that these 'subspecies' have diverged from one 

 another in respect to characters which have varied quite independ- 

 ently. There is no single graded series for all the characters — ," 

 loc. cit., p. 205. 



My proposition as to the use of subgenera in the case of large, 

 heterogeneous genera is in accordance with the practice which is pur- 

 sued at times by some systematists. The master-student of sponges, 

 F. E. Schulze, in a parallel case, though one dealing with subspecies, 

 thus marks out the treatment which he proposes for a horny sponge, 

 Hircinia variabilis. In the first place he combines six recorded 

 species, and then goes on to say "The older specific names of Schmidt, 

 like dendroides, flavescens, may be employed as varietal names for 

 certain conspicuous combinations of characters which frequently oc- 

 cur in particular localities, but which are by no means constant. 

 Thus we may speak of a Hircinia variabilis dendroides, a Hircinia 

 variabilis flavescens, etc. But ivhen a specimen does not conform 

 to one of these types, ive will have to designate it simply as Hircinia 

 variabilis.'"^ (Italics, except for names, mine.) 



Chapel Hill, N. C. 



' H. S. JenninKs 1917. Observed Changes in Hereditary Characters in relation to Evolu- 

 tion. Journ. Wash. Acad. Sci., Vol. VII. 



'P. B. Summer 1918. Continuous and Discontinuous Variations and their Inheritance 

 in Peromvscus. Amer. Naturalist. 1918. 



*F. K. Schulze 1879. I'ntcr.s. ij. den Bau u. die Kntw. d. Sponpien VIII. Die Gattung 

 Hircinia Nardo uiid Olifcoceras n. g. Zcit.sohr. f. wi.ss. Zool. Bd. XXXIII, p. II. 



