334 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



(1.) If Balfour (2) says that the ciliated cells which cover the 

 ciliated chambers or radial tubes of the Sponges undoubtedly 

 originate from the invaginated cells (i.e., the ciliated cells of the 

 Ectoderm), then I would like to state that they certainly did not 

 originate from those, they are moreover in Sponges and Ccelenterata 

 modified elements of the Ectoderm which may be produced 

 originally from the Ectoderm in some cases, (invagination) but not 

 necessarily must be produced by the Ectoderm (delamination.) 



If we once more compare the canal system of Sponges and 

 higher Ccelenterata, we shall see that it can open outward free in 

 both, that it can be covered with entodermal ciliated cells for a 

 greater or smaller extent, and that lastly it can take up nourish- 

 ment through its tei'minal pores in both. 



Another reason which is generally brought forward against the 

 Ccelenterate nature of the Sponges is, that the Sponges never 

 possess tentacles or Cnidoblasts. 



Without placing too great a weight on the want of both in 

 Beroe' which is a rudimentary form in this respect I only wish to 

 discuss : Have the ancestors of the Sponges ever possessed 

 tentacles and Cnidoblasts ? and if yes, how have they lost them ? 

 If no, why were these not attained in the course of time. 



Cnidoblasts or their Homologa, respectively Analoga and 

 tentacles are so widely spread among low marine animals, and 

 are met with in so very different animals, that they cannot be 

 used as a determinant for the relationship, as they are arrange- 

 ments doubtlessly often attained sua sponte. But as they are met 

 with in higher Ccelenterata (3) in different modifications, nearly 

 without exception, they appear to be a very old peculiarity of these 

 animals, which has proved itself as very useful in the struggle for 

 existence, and which therefore could find such a wide distribution 

 by heredity, in some cases perhaps by an adaptation sua sponte. 



(1.) Kiilliker. Icones Histological. 1 Heft., p. 66. 



(2.) F. Balfour, I.e., Vol. I., p. 144. 



(3. ) Which might be separated from the Sponges as Telifera or as Nemato- 

 phora, Huxl., (because the name Cuidaria, nettle animals does not cover 

 the meaning.) 



