REPORT ON THE CALCAREA. 21 



be disputed. We come, therefore, in accordance with Prof. Haeckel, to the conclusion that 

 to the properties of the canal system the greatest systematic value must be assigned. 

 It is, however, not to be forgotten that in different cases this value is not equal 



The canal system of the Leucones is nothing but a simple modification of that of the 

 Sycones, and a modification in the direction of a further development. Not so with the 

 Ascones as compared with the Sycones. As I endeavoured to show when discussing 

 the question of the affinities of the Calcarea amongst themselves, the canal systems of 

 both these families are products of quite different modes of development, that of the 

 Ascones presenting a modification in one direction, that of the Sycones in another ; 

 and if we now give expression to this phylogenetic difference, the division of the 

 Class Calcarea into two Orders becomes necessary. 



But it is high time to state the arguments which lead me to regard the Calcarea 

 as a Class and not as a Sub-class or Order. Of course, the systematic position of the 

 group Porifera in the animal kingdom is at present ambiguous. It is, however, clear 

 that, if the group is to be regarded as an independent type, this type is not to be 

 opposed to all the other types combined, as Balfour has proposed, and, on the other 

 hand, if the sponges are to be united with Ccelenterata, this could take place only 

 if they were erected into a separate sub-type within this type. As far as the well- 

 known hypothesis of the late Prof. Balfour 1 is concerned, I refer the reader to a 

 detailed critique in Mr. Marshall's 2 paper "On the ontogeny of Reniera filigrana." 

 What I may have to add on my own part will not occupy more than a few words. 

 Balfour sees in the Amphiblastula a colony of Infusoria, and founds his further conclusi< >u* 

 mi the fact that the cells in the larva which become invaginated are not coarse-grained 

 and dark- coloured, but transparent monociliated cells of cylindrical form (E. Metschnikoff, 3 

 F. E. Schulze 4 ). It is, however, questionable whether the Amphiblastula is really a larva 

 of primary characters. 



There are Calcarea whose development is marked out by a larva of quite different 

 type (Parenchymula), and MetschnikofFs Vergleichend-embryologishe Studien 5 make 

 it very probable — if not certain — that it is indeed Parenchyniula that shows the most 

 primitive features of aMetazoon ; and as the Blastula of the Calcarea in question presents 

 a vesicle whose cellular elements do not differ one from another, it is evident that the 

 chief character of the Amphiblastula is of a secondary nature. Its further development, 

 viz., the invagination of the clear cylindrical cells, is indeed very striking, but this 

 phenomenon is also common to the development of some other animals [Lumhricus, 

 Kowalevsky, 6 Oxyuris, Natanson 7 ), and this latter circumstance renders its value for 

 any phylogenetic speculations still more dubious. 



1 Quart. Jouni. Micr. Sci., vol. xix. p. 103, 1879. 2 Zeitschr. f. u-iss. Zool, Bd. xxxvii. p. 240, 1882. 



: » Ibid., Bd. xxiv. p. 1, 1874. 4 Ibid., Bd. xxxi. p. 262, 1878. 



6 Ibid., Bd. xxxvi. p. 433, 1881 ; Bd. xxxvii. p. 286, 1682. 6 Mint. Acad. St. Petersb., ser. 7, t. xvi.Mem. 12, p. 22. 1871. 



, Trans. Fifth Meeting of Naturalists in Warsaw, Sect, of Zool. and Comp. Anat. (Russ.). 



