igos\ Wilson — Sponges. 41 



Ihenea, is another instance of the same phenomenon. A 



complex instance of correlated variation is afforded by the 

 dermal and g-astral pinules of Caulophacus schulzci, which 

 coat the opposite :s (pore and oscular) of the body. 



The two kinds of pinnies vary in the same direction in differ- 

 ent individuals, and thus the proportionate difference between 

 them is preserved. 



6. Qualitative van a lion. 



Two sets of individuals living* tog-ether in the same locality, 

 and which are otherwise indistinguishable, differ conspicu- 

 ously in respect to a single point. An instance is afforded by 

 Kurctc credit in mucronatum, which differs from Euretc ore/ urn 

 tubulifcrum in having- oxyhexasters instead of onychasters. 

 Another instance is afforded by Tophon lamella indivisus^ 

 which differs from IopJion lamella only in the character of the 



bipocillus, which is not chelate. 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 

 dog-matize 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 dif- 

 ference is the duty of the systematist, who, when he has done 

 so, has pointed out an additional case suitable for the exper- 

 imental study of heredity and environmental action. 



7. I T ariation towards other species or subspecies. 



A class of spicules in one subspecies may vary in consider- 

 able number towards a condition characteristic of a subspecies 

 inhabiting- a different locality. An instance is afforded by 

 Euretc crectum gi'acile, in which the tuberculation of the g-as- 

 tral pentacts and hexacts is sometimes very similar to that 

 found in the other subspecies of Eurete crectum. 



Or a form of spicule characteristic of one species may occur 



