STUDIES ON THE COMPARATIVE ANATOMY OF SPONGES. 187 



perfectly straight, unbranched, and radially arranged. They 

 do not touch one another at all, and there is no trace of a 

 dermal cortex, hence there is no enclosed system of inhalant 

 canals, but the water circulates freely between the chambers 

 without any interruption. Sycetta appears to be the only 

 genus in which this most simple condition is retained. 



Stage B (Sycon stage). — This stage diflfers from the fore- 

 going only in the more or less complete fusion of the walls of 

 adjacent radial chambers wherever they come in contact. This 

 results in the formation of more or less well-defined inhalant 

 *' inter-canals." The chambers may also branch. In this 

 stage we find most species of the genus Sycon, and we may 

 perhaps also include Sycantha. Those species of Sycon in 

 which a thin pore-bearing membrane covers over the ends of 

 the " inter-canals,^^ as described above, are intermediate be- 

 tween stages B and C, 



Stage C (Grautia stage). — The chambers are still elon- 

 gated and radial, but their distal ends and the ends of the 

 " inter-canals '' between them are covered over by a dermal 

 cortex, which contains true inhalant pores, and sometimes a 

 complicated cortical inhalant canal system. In this stage we 

 find Grantia, Grantiopsis, Ute, Synute, Utella, Ana- 

 mixilla, Sycyssa, Grantessa, Heteropia, Heteropegma, 

 AmphoriscuSj and Syculmis. 



Stage D (Sy He ibid stage). — The chambers are no longer 

 arranged radially around the central gastral cavity, but are 

 still more or less elongated, and arranged radially around the 

 usually radial exhalant canals. It was this condition, first 

 described by PolejaefF (8), which gave rise to von Lendenfeld's 

 Sylleibidse (10, 11). It is not, however, characteristic of any 

 particular genus, much less of any particular family, but is 

 found in a few isolated species, such as Leucilla uter, 

 Leucandra aspera, and Vosmaeropsis macera. 



Stage E (Leucandra stage). — The chambers are small, 

 more or less spherical, and irregularly scattered through the 

 sponge wall ; and the inhalant and exhalant canal systems are 

 correspondingly developed. We find this condition in most 



