1884.] 49 [Hyatt. 



13, 1863. 1 A very clear and convincing series of observations 

 with figures has just appeared (Mem. Bost. Soc. Nat. Hist., 

 vol. in, no. 8, Development of Oecanthus and Teleas, p. 236, 

 1884) showing that the blastoderm is formed from amoeboid 

 cells, which look and act like these animals and assimilate the 

 yolk cells among which they first arise. The tissues of the Met- 

 azoa were, therefore, either derived from Amoeboid forms or 

 from these indirectly through the Flagellata and Ciliata. 



The p-3sence of collars and flagella, the internal structure 

 of the ceils of the ectoderm in the larvae of Silicea and Kera- 

 tosa and some Calcarea, the reappearance of these cells through- 

 out the interior of the lower Calcarea, and more localized in the 

 ampullaceous sacs of the remaining sponges, and the universality 

 and importance of intra-cellular digestion as carried on by these 

 cells in the sponges, — these are strong morphological and physi- 

 ological arguments for the immediate derivation of the sponges 

 from the Protozoa Flagellata. These lose none of their force from 

 the prevalence of flagellate cells in the tissues of other and higher 

 animals as in Hydra, Actinozoa, etc.; the fact remains that the 

 sponges are mainly, perhaps wholly, dependent upon intra-cellu- 

 lar digestion, and that the whole organization is a sieve with a 

 gastro-vascular water system adapted in the most direct manner 

 to the efficient performance of this function. As we shall also 

 try to show, the embryo is entirely peculiar in development 

 as compared with other allied types, and gives good ground for 

 the opinion, that the Porifera are not degraded forms of Meta- 

 zoa, but a normal progressive type on the lower borders of the 

 Metazoa and still retaining some of the primitive characteristics 

 and histological structure of the transitional types of the colonial 

 Protozoa Flagellata. 



This conclusion, however, is not so secure as one at first imag- 

 ines. It is perfectly well known that similar forms, structures, and 

 organs appear and reappear in different groups of the same stock, 

 while these forms, structures and organs could not possibly have 

 been derived by inheritance from the common stock, which did not 

 have them. They must have arisen independently in each of the 



1 r lhe best sumrrary of this subject with new observations is given by Bobretsky, 

 Zeitschr. wissensch. Zool., vol. xxxi, p. 195, 1878. 



PROCEEDINGS B. S. N. H. VOL. XXIII. 4 DECEMBER, 1884. 



