236 THE AMERICAN MUSEUM JOURNAL 



composition of the sponge skeleton. The latter basis is still used 

 for the division into classes, but the former has been for the most 

 part abandoned on account of the plastic nature of the frame- 

 work of sponges and the consequent variability of their growth- 

 habits. Such internal features as the form and arrangement of 

 the spicules, the extent of the choanocytic layers, and the general 

 plan of the canal system, seem to be more constant characters, 

 and are utilized in all recent classifications. There is, however, 

 much variability among internal characters also, and there are 

 yet many perplexing problems to the spongologist, especially on 

 accotmt of the great number of intermediate forms and unexpected 

 relationships. In fact a genealogical diagram of the sponges 

 would not so much resemble a branching tree, as a network with 

 connecting fibers anastomosing in all directions, and most prob- 

 ably approximating in its appearance the bewildering skeletal 

 labyrinth of the fibrous sponge itself. The following s5moptic 

 table, modified from Delage and Herouard, seems to be for the 

 most part in harmony with recent researches, and as likely as any 

 to have some degree of permanence, as it is largely based on 

 internal structure, i. e. the skeleton and canal systems: 



PORIFERA. 



No nematocysts, no mouth, but with inhalent pores; a cloacal 

 atrial cavity with a simple or multiple osculum ; a mesoderm. 



A. Class CALCAREA. Spicules calcareous; choanocytes large. 



a. Order HOMOCCELIDA. Atrial cavity lined with choanocytes. 



{Leucosolenia* Ascetta, Ascyssa, Hontoderma.) 



b. Order HETEROCCELIDA. Atrial cavity lined with pinacocytes 



(pavement cells), the choanocytes being withdrawn into radial 

 diverticula or ciliated chambers. {Sycon, Grantia* Uie, Bar- 

 rois-ia, Leucilla, Leucandra, Eilhardta, Eudea, Petrostoma.) 



B. Class NON-CALCAREA. Skeleton of silicious spicules, or of spongin 

 fibers or no skeleton. Choanocytes small. 



I. Subclass TRIAXONI^. Ciliated chambers large, elongated! 



skeleton of triaxial spicules or none. 

 . a. Order HEXACTINELLIDA. Skeleton formed of spicules. 



(i) Suborder Lissacina. Spicules independent during growth. 

 {Enplectella* Askonema, Rosella, Lophocalyx, Hyalonema* 

 Semper ella.*) 

 (2) Suborder Dictyonina. Spicules united during growth to 

 form a rigid trellis-work. {Farrea* Aphrocallistes* Hex- 

 actinella* Dactylocalyx, Ventriculites, Cceloptychium.) 

 * Represented in Museum Collection. 



