THE SPONGES. 



variation in the number of spicules which combine to form the side of a 

 skeletal mesh, p. 145. 



3. Uncorrelated variation in the mcgascleres of an individual, i. e. variation 

 apparently not correlated with the structural peculiarities of the body- 

 locality. 



As regards size of the spicules, there seems to be noticeable variation 



in all sponge species. The shape of one of the macramphidiscs varies 



considerably in Hyalonema bianehoixdum, p. 20. In CaHlo2)haciis schulzei 



the principal hexacts are occasionally tuberculated, p. 40, and in the same 



species the tuberculation of the pentacts varies, p. 43. The character of 



the diact ends varies commonly, e.g. in Bcdhjdorus Icris spimsns, p. 49. 



In Farrea mexicana the pentacts vary in respect to tuberculation, p. 56. 



In Euretc eredum the character of the distal ray of the gastral 



pinnies varies extensively, p. 62 (comp. F. E. Schulze, 1899). In 



Petrosixi variabilis crassa the oxea sometimes assumes the shape of a stron- 

 gyle, or style, p. 115. In Penarcs foliafonnis the triaenes vary con- 

 siderably, p. 109. In Pacli/fchalina aeapulcensis the size of the oxea 



varies within wide limits, p. 121. In Phakellia lamelligera the oxeas 



and the two kinds of styles all vary considerably in shape, p. 152. 



.^. Uncorrelated variation in the microsclercs of an individual. 



The inicroscleres as well as the megascleres very commonly vary in size 

 and detailed .shape, although in them, as in the megascleres, there is a 

 size and pattern which are characteristic of the individual (species), i e. to 

 which the majority of the spicules of an individual conform. 



Some striking cases of variation are afforded by the micro-oxyhexacts 

 of ILjalonema bianchuratum, p. 19, plesiasters and spirasters of Thenea fen- 

 estrata, p. 86, sigmata of Tglodesma alba, p. 133. 



5. Correlated variation in the sjncules. 



In some cases the variation of spicules is obviously not nngoverned by 

 the rest of the body, but is correlated with body-locality. 



Thus while the pentacts in Hexactinella lahyrinthica vary at large in 

 respect to length of the several rays, the pentacts overlying the larger 

 inhalent canals commonly have noticeably short proximal rays. Such a 

 phenomenon would customarily be referred to as " adaptive." The vari- 

 ation of dichotriaenes toward the protriaene type, round the pore areas 

 of Thenea, pp. 85, 89, 92, 95, is another instance of the same phenom- 

 enon. A complex instance of correlated variation is afforded by the 



