154 NATURE AND AFFINITIES OF THE SPONGES. 



sponges to certain Flagellate Protozoa being, on the other hand, so distinct 

 and decisive as to forbid their logical inclusion among the representatives 

 of any other organic class. 



The year 1872 is, perhaps, more notable that any in the entire annals 

 of sponge biography through the publication of Professor Haeckel's truly 

 magnificent work of labour and art, if nothing more, entitled 'A Monograph 

 of the Calcispongiae.' This treatise, as its name denotes, embraced an 

 exhaustive account of every known form and variety of sponge charac- 

 terized by the possession of a skeleton composed of spicules of carbonate 

 of lime, and of which the little white Grantia compressa of our own 

 coast affords a familiar example. The chief interest of this monograph, 

 however, depends upon the fact that it is made the vehicle of Professor 

 Haeckel's more matured views concerning the near relationship affirmed 

 by him to subsist between the sponges and the corals, and which he now 

 sought, by means of the sponge-group monographed, to establish on a 

 more firm and solid basis. This remarkable work has in other words 

 to be regarded as embodying the veritable consummation of his then 

 newly conceived and now world-familiar "Gastraea" theory, having as 

 its aim the demonstration that all animal forms, from the sponges up 

 to the Vertebrata, emanate in their developmental history from one 

 single stock-form or phylum, upon which the common title of a "gastrula" 

 is conferred. This gastrula, as formulated by Haeckel, is constructed 

 fundamentally upon the same type as the advanced condition of the 

 embryonic planula, having an ovate body composed of two even, separate 

 cellular layers, the ectoderm and endoderm, and a central primitive 

 stomach-cavity or archenteron, which communicates at one extremity 

 with the outer world by a primitive oral orifice. From this identity of 

 the bilaminate gastrula in representatives of the most various animal 

 stocks, from the sponges to the Vertebrata, Haeckel, to quote his own 

 words, deduced the common descent of these various animal phyla from 

 a single unknown stock-form, his hypothetical gastraea, which was con- 

 structed on a plan essentially corresponding with the above-described 

 typical gastrula. As a first step towards the successful correlation of his 

 gastraea theory with the group of organisms now under consideration, it 

 necessarily devolved upon Professor Haeckel to refute the more recent 

 interpretations, still adhered to by many authorities, which relegated the 

 sponges to the lowermost or Protozoic section of the organic series. At 

 the least, it was to be expected that this eminent author would devote 

 some little space to the serious discussion of the new and very im- 

 portant facts concerning the ultimate structure of sponges and suggestive 

 affinities elicited through the investigations of Professor H. James-Clark 

 and Mr. Carter. In place of this, no consideration whatever is given 

 to their discoveries, which are brusquely dismissed with the comment that 

 neither one nor the other of these authorities have any conception of 

 the essence of the cell-theory. The present author is visited, for his 



