INTEODUCTION. 



vera plantce qua metamorpliosi transeunt in flores animates (vera 



In spite, however, of the influence of the great Swedish 

 systematist, naturalists had come before the end of the eighteenth 

 century to a general agreement as to the animal nature of these 

 plant-like structures, which were all associated together under 

 the name zoophytes. That this was not a single homogeneous 

 group, was known to some last-century observers. Spallanzani 

 remarked that the polypi are independent, and are bent in their 

 cells like a bow, instead of being continuous downward into the 

 central fleshy axis, as they are in such zoophytes as Sertularia. 

 Loefling 1 pointed out that in Flustra pilosa the different polypi 

 (zocecia) act independently, and that the irritation of one does 

 not cause them all to withdraw into their cells, as it does in such 

 forms as Sertularia. These observations prepared the way for the 

 work of those who by description of the anatomical structure of 

 these animals, showed that the polypes are based on several very 

 different plans. 



Renier, 2 in 1793, discovered that some of the zoophytes agree 

 in anatomical structure with Ascidia, and not with Hydra ; in 

 consequence one group was transferred to the Mollusca. Grant, 3 

 in 1827, described the animal of Flustra, and showed that it is 

 equally advanced above the Hydra type. His work was followed 

 by that of Vaughan Thompson 4 on some species of Sertularia, the 

 cells of which he found to be inhabited by a new animal, the 

 Polyzoa, " which agrees more closely with the AscidiaB than with 

 the Hydrae." He suggested that the "species of Sertularia in 

 which the animals have been determined to be Polyzoae may 

 perhaps be referred to one genus," which he separated from 

 Sertularia under the name of Vesicularia (op. cit. p. 97). 



1 Pehr Loefling. Beskrifning pa tvaenne sina Coraller : Handl. k. Sven. 

 Vet. Acad. vol. xiii. (1752) pp. 109-22, pi. iii. 



2 Benier. Opusc. Scelt. t. xvi. p. 256, t. 1. 



3 R. E. Grant. Observations on the Structure and Nature oiFlustra : JSdinb. 

 New Phil. Journ. vol. iii. (1827) pp. 107-18, 337-42. 



* John Vaughan Thompson. On Polyzoa, a new animal discovered as an 

 inhabitant of some Zoophites with a description of the newly instituted Genera 

 of Pedicellaria and Vesicularia, and their species : Zool. Researches, No. v. 

 pp. 89-102, pis. i.-iii. 



