The Skeleton and Classification of Calcareous Sponges. 75. 



Genus 2. Heteropegma, Pol. The external surface is a cortex 

 with dermal skeleton, and the ends of the branches 

 are indistinguishable as separate prominences. Sp. : 

 Heteropegma nodus gordii. 



(From Dendy's illustration it would seem that his Leucandra aus- 

 traliensis ((17) Fig. 17) should form the type of a third genus in this 

 family, with a dermal membrane but no cortex.) 



It is impossible to estimate the degree of relationship between 

 Calcaronea and Calcinea until the histology of siliceous sponges is 

 better known. The fact that the skeleton is in both groups composed 

 of calcite seems little evidence of common origin ; since the researches 

 of Ebner and Minchin suggest that they separated before the calcite 

 took the form of spicules. The mode of attachment of the flagellum 

 would seem necessarily perfected so soon as the mode of nourishment 

 by aquiferous canals was established for the race ; on this reasoning it 

 would seem not improbable that the phylum Sponges may be com- 

 posed of two classes, the Basinucleata and the Apicinucleata ; or the 

 Hexactinellida may be a third class of equal value. The Spongil- 

 Iida3 and Spongida are the two groups among Demospongia3 which 

 would appear to offer themselves for union with the Calcinea, as 

 having basal nuclei to their collar-cells and larvas completely 

 flagellate ; for the Apicinucleata we know of distal nuclei in the 

 Calcaronea, Halichondria (18) and probably (reasoning from Schulze's 

 figures) Chon'lrosia (3), Corticium (6), Halisarca (3). 



The Spongillidaa and Spongida are both anomalous groups, and 

 the Demospongise would be rather more homogeneous if they were 

 removed, and scarcely more heterogeneous by the admission of the 

 Oalcinea. But our knowledge is as yet too imperfect to propose 

 such a classification. 



List of works referred to. 



<(1) Miklucho-Maclay . . . . 1868 " Beitrage zur Kenntniss der Spongien," ' Jen. 



Zeits.,' vol. 4, p. 221. 



(2) Schmidt, 1875 ' Zeits. Wiss. Zool ,' vol. 25. Appendix, p. 132. 



(3) Schulze, F. E 1877 " Untersuchungen iiber den Bau und die 



Entwicklung der Spongien. II. Die Gat- 

 tung Halisarca" 'Zeits. Wiss. Zool.,' vol. 

 28, p. 1. 



" Untersuchungen u. s. w. III. Die Familie 

 der Chondrosida;," 'Zeits. Wiss. Zool.,' 

 vol. 29, p. 87. 



(4) Keller 1878 Zeits. Wiss. Zool.,' vol. 30, p. 585. 



(5) Metsclmikoff, E. ... 1879 " Spong. Studien," ' Zeits. Wiss. Zool.,' vol. 32, 



p. 349. 



