10 



THE SPONGES. 



dermal and gastral pinnies of Caulophacus schuhei, which coat the opposite 

 surfaces (pore and oscular) of the body. The two kinds of pinnies vary 

 in the same direction in different individuals, and thus the proportionate 

 difference between them is preserved, p. 42. 



6. Qualitative variation? 



Two sets of individuals living together in the same locality, and which 

 are otherwise indistinguishable, differ conspicuously in respect to a single 

 point. An instance is afforded by Eurete erectum mucronatum, which differs 

 from Eurete erectum tubuliferum in having oxyhexasters instead of onychas- 

 ters, p. 64. Another instance is afforded by Iophon lamella indivisus, which 

 differs from Iophon lamella only in the character of the bipocillus, which is 



not chelate, p. 145. 



In order not to confuse the facts with hypothesis, 



the two sets of individuals have in each case been separated as subspecies. 

 It is idle to dogmatize or to speculate in extenso on the value, from the 

 standpoint of heredity, of the point of difference. Whether this point is 

 inheritable and thus marks off two races, or whether it merely marks off 

 two sets of individuals which started out alike and the offspring of which 

 are alike, and which owe their difference to the action on the individual 

 of the environment, no one can say. The recording of the difference is 

 the duty of the systematist, who, when he has done so, has pointed out an 

 additional case suitable for the experimental study of heredity and environ- 



mental action. 



7. Variation towards other species or subspecies. 



A class of spicules in one subspecies may vary in considerable number 

 towards a condition characteristic of a subspecies inhabiting a different 

 locality. An instance is afforded by Eurete erectum gracile, in which the 

 tuberculation of the gastral pentacts and hexacts is sometimes very similar 

 to that found in the other subspecies of Eurete erectum, p. 66. 



Or a form of spicule characteristic of one species may occur infrequently 

 in a related species. For instance, in Caulophacus schukei the pinuli occa- 

 sionally have the shape characteristic of C. latus and C. elegans, p. 42. A 

 striking case is afforded by Farrea occa claviformis, in which a few gastral 

 clavulae were found closely similar to the peculiar clavulae of Farrea con- 

 volvulus, p. 55. 



8. Constancy of character in spicules. 



It often happens that while in a single individual the size of a particular 

 spicule may vary within wide limits, the character remains fairly constant, 









