248 ARTHUR DENDY. 



radiate Homocoelous form as this that the Heteroccela have 

 probably been derived. I do not by any means wish to single 

 out Leucosolenia tripodifera itself as the ancestor of the 

 Heterocoela, for I do not for a moment believe that it is so. 

 The copious branching of the radial tubes, and the fusion of 

 adjacent tubes at the points of contact, indicate a more 

 advanced condition in some respects than is met with in the 

 simplest Heterocoela (Sycetta). The youngest part of the 

 sponge, nearest to the osculum, where the radial tubes are still 

 simple and unbranched, makes a much nearer approach to the 

 hypothetical ancestral form. 



In any case, the simple radiate type of structure, though 

 perhaps no more highly specialised than certain other types 

 met with amongst the Homocoela, appears to form the natural 

 starting-point for all the divers types met with amongst the 

 Heterocoela, with the probable exception of Leucascus, to 

 which 1 shall refer again later on. The simpler forms of 

 Heterocoela still preserve the radiate character, which becomes 

 at first even more pronounced in the structure of the skeleton. 

 It is also a most important and significant fact, that in the 

 ontogeny of these simple Heterocoela the radial tubes 

 (flagellated chambers) are formed as outgrowths from a central 

 tube, exactly as in Leucosolenia tripodifera. An excellent 

 illustration of this mode of formation is given by Korschelt and 

 Heider (2). 



I ought, perhaps, in this place to say something about Dr. 

 von Lendenfeld's supposed families " Homodermidse ^' and 

 " Leucopsidse." I have, however, already expressed my views 

 on this subject in an earlier paper (1), and those views I still 

 maintain, for I cannot see that there is anything in Dr. von 

 Lendenfeld's observations, including those published in " Die 

 Spongien der Adria " (10), to justify us in accepting these 

 families. It would take too long to argue the question here, 

 and I am quite content to refer the reader to Dr. von Lenden- 

 feld's own writings. 



I maintain, then, that the ancestral form of the Heterocoela 

 was a simple, radiate, Homocoele sponge, simpler even than 



