OBSERVATIONS ON POLYZOA-. 159 



but it cannot be said with certainty, that all the individ- 

 uals of the species are the same, since no direct observa- 

 tions have been made upon this character. Perfect radia- 

 tion is essential to the structure of Pectinatelia and Cris- 

 tatella. The internal divisions, and the regular outlines 

 of the coenoecia give a more decided radiation to the colo- 

 nies of Pectinatelia and Cristatella than to those of pre- 

 ceding genera. 



This more perfectly radiatory arrangement is directly 

 traceable to the larger number of buds developed from 

 the original cell, since instead of one or two buds as in 

 Fredericella, there are five or more which spring from the 

 walls of the primary cells in Pectinatelia, and in Crista- 

 tella probably even a larger number. This radiatory 

 character, therefore, which distinguishes individual varie- 

 ties in Fredericella and Plumatella, is of generic value 

 in Pectinatelia and Cristatella, 



Adherent, The hardness of the ectocyst determines 

 the tenacity with which the branches cling to surfaces. 

 The brown, horny ectocyst of the Fredericellaj anchor 

 them very firmly ; but there are some transparent colo- 

 nies in this genus, and these are not so strongly fastened ; 

 in Fredericella pulcherrima the latter are quite numerous. 

 Among the Plumatella? there a-re more or less of the 

 transparent colonies in ever}^ variety, and Plumatella 

 vesicularis and P. vitrea have, in all cases, transparent 

 ectocysts. 



According to Prof. Allman, the gelatinous ectocyst of 

 Lophopus is easily detached, and the ectocysts of Pectin- 

 atelia or Crista-tella are by no means as tenacious of their 

 hold upon the surface as the ordinary brown ectocyst of 

 the Plumatellae. The hardness of the ectocyst, also, de- 

 termines the tenacity with which it and the endocyst cling 

 together. In Pectinatelia the endocyst readily separates 

 from the gelatinous base, and Cristatella moves freely 

 upon the surface of its own ectocyst. The ectocyst and 

 endocyst of variety c of Plumatella vitrea invariably sep- 

 arate when treated with alcohol. In the brown varieties 

 of Fredericella and Plumatella such a rupture is much 

 more difiicult to accomplish. 



