68 SYNOPTIC COLLECTION. 



The* primitive and most generalized Porifera must be 

 those sponges that in their adult form and characters 

 most nearly approach the gastrula-like embryo. It will 

 be seen that such sponges are the Calcarea or the group 

 of calcareous sponges next to be described. 



CALCAREA. 



It cannot be doubted that a form existed in the past 

 (if it is not living at the present time) which possessed 

 the simple structure of the generalized Calcarea, but 

 which was without a skeleton of any kind and also with- 

 out the power of taking up foreign matter to make one. 

 Such a sponge would be a primitive one, and its develop- 

 ment would throw much light on the origin and classifi- 

 cation of the Porifera. Until this gap is tilled we must 

 begin with Prophysema primordiale Hkh (PI. 60). 1 Al- 

 though this sponge never develops a skeleton, yet it pos- 

 sesses the capacity, exhibited by a few other sponges and 

 by some Protozoa, of taking up foreign substances (in 

 this case both silicious and calcareous spicules) and of 

 making a false skeleton sufficient for the support of its 

 own body. 



Prophysema is a simple attached tube with one open- 

 ing, and with the body cavity lined with flagellate cells. 



iThis form was previously described by Haeckel as Haliphysema 

 primordiale Hkl. (Jena. Zeitschr., XT, 1877). According to Kent, 

 E. Ray Lankester, and Mobius, the type species of Haliphysema 

 (H. tumanowiczi) is a Protozoan of the Rhizopod group. Haeckel 

 now agrees with these authorities that the interior of this last 

 named species is filled with protoplasm which extends from the 

 single opening in the form of pseudopodia and that, therefore, this 

 form is a Rhizopod, but he also maintains that in the species for- 

 merly called Haliphysema primordiale but now named Prophysema 

 primordiale there is a distinct body cavity lined with flagellate epi- 

 thelium, so that this species is a true sponge. For further informa- 

 tion see Rep. Chall. Exp., Zool., XXXII, part 82, 1889, p. 26. 



