20G Professor Link's Observations on Zoophytes, 



motion were detected in the sponges, he considers that this 

 would not be sufficient to establish their animal nature, for 

 the same has been noticed in confervae. He thinks that the 

 absence of polypi, the existence of distinct sporangQs in the 

 Spongilla, and the analogy between the latter and true 

 sponges are sufficient to separate the sponges from the 

 Zoophytes and to class them with the Algae. 



It is true that the structure of sponges is different from 

 that of other algae, but the structure of the latter presents 

 striking modifications. Grant has observed in sponges 

 very fine points formed of pure silica, which correspond 

 with the fine fibrous points which we observe in the spon- 

 gilla, and which possess equal solidity and tenuity. In 

 other respects these plants approach near the first animals. 

 They are composed of a thick tissue, consisting of filaments 

 and tubes as in sponges, which is less reticulated, and is not 

 covered by a gelatinous membrane. The tubes are covered 

 with spiral points which are the commencement of the 

 branches. In some cases we remark elongated branches. 

 They are perfectly transparent, tenacious, and dissolve with 

 effervescence in dilute muriatic acid, leaving only a slight 

 portion of membrane. 



They are, therefore, covered with carbonate of lime com- 

 pletely transparent, which is rarely met with in the Zoo- 

 phytes. 



But the animal nature of these beings is proved by the 

 large cavities, which occupy not only the interior of the 

 youngest branches in the Alcyonium arboreum, but which 

 are prolonged through the crust to the surface, where they 

 terminate in polypi. 



Hence, we see how slight is the distinction between 

 plants and animals. 



The animal matter is so to speak opposed to vegetable 

 substance. The first disappears in the sponges, and vege- 

 table matter remains. 



Olivi and Bertolini consider the Nullipores as calcareous 

 deposits. Schweigger takes them for Zoophytes, which are 

 transformed immediately after their production into cal- 

 careous matter. He cites, as a proof of this opinion, that 

 after having placed them in muriatic acid, a gelatinous 

 body still remained of the figure of the Nullipores. 



