NATURE AND AFFINITIES OF THE SPONGES. 169 



attention to the more important structural features exhibited by the leading 

 subdivisions of the Spongida, and especially to those points in which their 

 close relationship to the independent collar-bearing monads figured in 

 the five preceding plates is most prominently shown. As already stated, 

 the collared cells or essential Spongozoa of any given sponge-body are 

 invariably found lining special chambers excavated within the common, 

 structureless, mucilaginous basis or cytoblastema which enters more or less 

 considerably into its composition. These special chambers, again, are 

 found in different sponges to exhibit a considerable diversity of contour, 

 but, on the whole, to conform to two distinct and widely differentiated 

 plans. In one of them it is found that the collared cells more or less com- 

 pletely line the entire internal cavities of the sponge, including both the 

 afferent and efferent canal-systems. Such a type of structure, as is most 

 prominently developed among the section of the Calcispongiae, is illustrated 

 in the sectional views given at PI. VII. Figs. 3 and 4, of the interstitial 

 canal-system and disposition of the characteristic collared monads or Spon- 

 gozoa in the familiar British species Grantia compressa. At Fig. 3 a general 

 view is given of the segment of a complete transverse section of this sponge, 

 showing the characteristic disposition of the interstitial loculi with their 

 monad linings around the common cloaca, while at Fig. 4 one complete and 

 another incomplete loculus is considerably enlarged, proving the essential 

 correspondence of the contained monads with the independent forms figured 

 in the preceding plates. In the series belonging to the second structural 

 plan, the collared cells, instead of being distributed more or less generally 

 throughout the entire internal canal-system, are confined to certain sphe- 

 roidal chambers excavated within the substance of the sponge body, these 

 chambers being brought freely into relation with the external water through 

 the agency of both the afferent and efferent canals. It was upon these 

 spheroidal chambers, as first discovered in Spongilla, that Mr. Carter con- 

 ferred the title of " ampullaceous sacs," by which name, together with that 

 of "ciliated chambers," they have since been most familiarly known. A 

 similar ampullaceous disposition of the collar-bearing cells is found to obtain 

 among a very extensive series, if not throughout the majority of the Spon- 

 gida, including, in fact, all the known members of the Myxospongia, the 

 greater part of the Siliceospongia, and in accordance with the representa- 

 tions given by Professor Haeckel, the family of the Leuconidae among the 

 Calcispongiae. The highly characteristic aspect presented by the collared 

 monads or Spongozoa, as grouped upon this principle, will be found deli- 

 neated at PL VII. Figs. I and 2, and PL IX. Figs. I, 3, and 12, and is 

 remarkable for the elegant clustered or grape-like appearance presented 

 by the monad aggregations with their interconnecting canal-systems. In 

 Fig. i of PL VII. is reproduced the portion of a section of the non- 

 spiculiferous sponge Halisarca lobularis as delineated by F. E. Schulze, 

 while at Fig. 2 is represented a somewhat similar section of the siliceous 

 type Esperia sp., as observed by the author. 



