60 COMPARATIVE ANATOMY CHAP. 



between these consists of branched and partly anastomosing cells, 

 which lie in a hyaline ground substance. The cells of the lowest layer 

 possess processes, which pass into the processes of the cells of the 

 middle layer without sharp distinction. As long as we Lave no know- 



FIG. 55. Part of a vertical section through the body of Trichoplax adhaerens, after 

 F. E. Schulze. 



ledge of the reproduction and development of this animal, judgment 

 as to its morphology must be suspended. 



[Note. Of. p. 175. Where the author suggests that the Dicyemidce and Ortho- 

 nectidce, on account of their similarity to the sporocysts, are degenerated Trematoda. 

 -Tr.] 



Literature. 



E. Haeckel. Biologische Studien. Heft II. 1877. 



Ed. van Beneden. Recherches sur Us Dicyemides. Bull. Academic Belgique. 



Bruxelles, 1876. 

 C. 0. Whitman. A Contribution to the Embryology, Life-History, and Classification 



of the Dicyemids. Mittheil. aus d. zool. Station zu Neapel. T. IV. 1882. 

 A. Giard. Les Orthonectides. Journal de I' Anatomic et de la Physiologic. T. XV. 



1879. 



E. Metschnikoff. Untersuchungen ilber Orthonectiden. Zeitschr. f. wiss. Zoologie. 



Bd. 35. 1881. 



Julin. Contribution & Vhistoirc des Mesozoaires. Archives de Biologie. T. III. 

 1882. 



F. E. Schulze. Ueber Trichoplax adhaerens. Zoolog. Anzeiger. Bd. VI. 1883. 



S. 92-97. 



CLASS II. Porifera or Sponges. 

 Systematic Review. 



Sub-Class I. Calcaria. Skeleton composed of spicules of carbonate of lime, 

 always present. According to the structure of the soft body, Ascones, Sycones, and 

 Leucones. Olynthus, Ascandra, Sycandra, Leucandra. 



Order 1. Calcispongige. 



Sub-Class II. Non-Calcarea. Skeleton seldom wanting, but never of calcareous 

 spicules, rather of siliceous spicules or spongin fibres. According to the structure of 

 the soft body, Leucones. 



