STUDIES ON THE COMPABATIVE ANATOMY OF SPONGES. 525 



this Sponge to the researches of Dr. Vosmaer (loc. cit. supra), 

 and I am able to do little more than confirm the results which 

 he has arrived at. 



As already stated, the canal system is lacunar. The scat- 

 tered pores (fig. 9, p.) lead into expanded subdermal cavities 

 (s. c.) lying between the tufts of spicules in the ectosome. 

 These in turn communicate with a system of more or less 

 lacunar inhalant channels in the choanosome. The inhalant 

 lacunae are separated from the exhalant lacunae by strands of 

 mesodermal tissue in which the flagellated chambers are em- 

 bedded (fig. 10,/. c). Many flagellated chambers communi- 

 cate directly with one and the same inhalant or exhalant 

 lacuna, but occasionally I have seen traces of what appear to 

 be short and rather wide canaliculi (fig. 10, a). These would 

 seem to be developed when the situation of the chamber 

 prevents it from opening immediately into a wide canal or 

 lacuna. 



The chambers themselves are usually somewhat elongated, 

 but their actual shape is a good deal affected by the state of 

 contraction of the tissues. Good-sized examples measure 

 about 0*045 mm. in length and 002 mm. in transverse 

 diameter. 



The exhalant channels open into branches of the oscular 

 tube, whence the water is discharged through the osculum. 



Thus it would appear that the canal system of Quasillina 

 belongs essentially, as stated by Vosmaer, to his third type, 

 while that of Rid lei a belongs to his fourth type. I believe, 

 however, that the canalicular and non-canalicular types of 

 canal system cannot be sharply defined from one another, and 

 that they will be found to pass by insensible gradations iDto 

 one another. 



General Conclusions. 



The genera Ridleia and Quasillina are shown by their 

 spiculation, skeleton arrangement, and general form to be 

 closely allied, and it is not until we have examined properly 

 prepared stained sections that we are able satisfactorily to 



