5 I 2 POLYZOA 



which in the Gymnolaemata forms a polypide-bud after' fixation. 

 The peculiarities of the Phylactolaematous larva may be explained 

 by assuming that it becomes a zooecium while it is still free- 

 swimming. Thus the larva of Plumatella develops one or some- 

 times two polypides, which actually reach maturity before fixation 

 takes place. That of Cristatella develops from two to twenty 1 

 polypides or polypide-buds at the corresponding period, and it is 

 in fact a young colony while still free-swimming. 



Now in most colonial animals, such as Coelenterates and 

 Ascidians, the larva metamorphoses itself into a temporarily 

 solitary animal, which then gives rise to the remainder of the 

 colony by budding. The majority of the Gymnolaemata behave 

 in this way ; while the Phylactolaemata may not only develop a 

 multiplicity of polypides in their larval stage, but the individu- 

 ality of the zooecia is then just as much obscured as in the adult 

 state. These facts are more easily explained if we assume that 

 Cristatella is the end-point in a series than if we suppose it to 

 be a starting-point. 



On the view maintained by many authorities, that the 

 Polyzoa are related, through Phoronis, with the Gephyrea and 

 the Brachiopoda, we should expect to find in those Polyzoa 

 which most closely resemble Phoronis in their adult state that 

 is to say in the Phylactolaemata some indications of affinity to 

 that animal in their development. This is emphatically not the 

 case. The hypothesis that the Phylactolaemata are related to 

 Phoronis leads, moreover, to the improbable conclusion that the 

 similarities between the Entoproct-larva and Cyphonautes, on the 

 one hand, and the Trochosphere larva of Polychaeta, on the 

 other hand, is entirely superficial and meaningless. In spite, 

 therefore, of the similarity between Phoronis and a single 

 individual of the Phylactolaemata, and in spite of the marked 

 resemblance between its nephridia and structures which have 

 been described in Cristatella 2 and Pectinatellaf the comparative 

 study of the development appears to indicate that the resem- 

 blances between Phoronis and the Phylactolaemata are the result 

 of a coincidence rather than of any close relationship. 



A few points connected with the metamorphosis of the 



1 Jullien, M6m. Soc. Zool. France, iii. 1890, p. 381. 



2 Cori, Zeitschr. wiss. Zool. lv. 1893, p. 626. 



3 Oka, J. Coll. Japan, iv. 1891, p. 109 ; viii. 1895, p. 339. 



