STUDIES ON THE COMPAEATIVE ANATOMY OF SPONGES. 21 



readily distinguished around the inhalant canals^ where they 

 are less obscured by spicules and other mesodermal structures 

 than on the dermal surface. The nucleus is surrounded by 

 the very characteristic granules described by Schulze in 

 Sycandra. In my preparations I have only after some 

 trouble succeeded in making out the boundary lines between 

 the individual cells^ and Schulze himself observes that it is 

 remarkable that the boundaries of these cells — sometimes so 

 distinct — are not always clearly visible. Nevertheless I have 

 been able to determine the shape of the cells pretty accurately, 

 and found them to agree precisely with Schulze's drawings. 



The Endoderm. 



This consists, as in other Heterocsela^ of two parts : (1) a 

 layer of flattened epithelial cells lining the gastral cavity and 

 the short exhalant canals of the chambers ; (2) a layer of 

 collared cells lining the flagellated chambers themselves. The 

 epithelial portion of the endoderm exhibits no features of 

 special interest and needs no further description^ so we may 

 pass on at once to the collared cells. 



Dr. R. von Lendenfeld has recently (16) called in question 

 the accuracy of my description of the collared cells, with their 

 connecting membrane^ in Stelospongos (2), observing, '^ Es 

 ist jedoch seine schematische Darstellung dieser Membran 

 (Taf. xxxii, fig. 9) keineswegs Vertrauen-einflosseud, sondern 

 eher ein Beweis der theoretischen Unwahrscheiulichkeit der 

 Existenz derselben." Notwithstanding this criticism, I still 

 maintain the correctness of my original description and figures, 

 and have already published a note (17) in the ' Zoologischer 

 Anzeiger ' in reply to Dr. von Lendenfeld's observations. The 

 latter are apparently based partly on imperfect observation, 

 and partly on the convenient, albeit somewhat uuphilosophical, 

 assumption that all sponges must be exactly alike in this 

 respect. Dr. von Lendenfeld finds that in certain sponges 

 examined by him " der Raum zwischen den Kragenzellen 

 von einer durchsichtigen, der gewohnlichen Gruudsubstanz 

 der Zwischenschicht der Spongien sehr ahnlichen Substanz 



