698 



RADIATA. 



CLASS POLYPI. 



Of this class, now more commonly termed Polypifera, mufh more is now knov^^n than was tnrnvQ 

 to Cuvier ; anl his classification has altogether given place to one in which the primary characters ar*^ 

 drawn from the structure of the animal, that derived from the compound mass qt polypidom being of 

 secondary importauce. The separation of the Carnusi or Actiniform polypes from the Gelatinosi or 

 Hydraforni polypes, was, as we shall see, quite correct; but, on the other hand, the separation of 

 the solitary genera from the compound forms of the same groups was altogether erroneous. Thus 

 among the Coralliferi of Cuvier, the greater part of the first family is composed of Hydraform 

 polypes ; the second is made up of one genus [CeUularia) which is not a Zoophyte at all, but a MoUus- 

 can, and of another (Corallina) which is now well ascertained to be of vegetable character ; whilst 

 the third is a heterogenous assemblage of MoUuscans, with Actiuil'orm and Alcyonian Polypes, and 

 Sponges. 



The primary division of the Cuvierian Polypifera is now generally admitted to be into Eryozoa and 

 Anthozoa ; the former being truly MoUuscans^ and properly forming part of the class Tuntcata; 

 whilst the latter are true Radiated animals. To the latter alone, therefore, ought the name of Zoo- 

 phytes to be restricted. Au outline view of the structure and classification of each group will now 

 be given. 



BRYOZOA. 



If we imagine the minute tentacula which fringe the oral orifice of mvLUj Ascidians to he greatly 

 prolonged and clothed with cilia, whilst on the other hand, the respiratory chamber or dilated pharynx 

 is contracted, we shall have the likeness in its most important characters, of the animal of the Fh/itraj 

 Bujverbankia, or any other Bryozoon It is not surprising that, until the structure of these animals 

 had been investigated, the stony and horny fabrics which they form should have been regarded as poly 

 pidfims. x^nd even since the wide differences in conformation between the Bryozoa and the Anthozoa 

 have been made known, the former as well as the latter have been frequently ranked among the Poly 

 piitra. The discovery of the gemraiparous development of the true Tunicata, however, has removed 

 one of the great boundaries that seemed to divide them from the Bryozoa ; whilst, 

 on the other hand, the existence of forms among the latter that present a very 

 ne^r approach to the former, and more especially the discovery that their nervous 

 system is not formed upon the radiated type, but consists of a single ganglion 

 placed between the two orifices, as in the Tunicata, have led to their entire 

 detachment from the class Polypifera, and their removal to the MoUuscan series. 

 The grounds of this separation, and the relations of the Bryozoa to the 

 Tunicata and Polypifera respectively, will be better understood when the 

 structure of the animals has been examined. To this, then-fore, we now 

 l-t'\J pruL'fL'd, taking as our type a very common British species, the Boireibankia 



■^ If 11 de/i^a, in which, from the isolation and transparency of the shell or sheath, 



tlie internal arrangement can be very distinctly seen. The animal of the 

 Jjoicerbaiifyia, when the tentacula are fully expanded, is about half an inch in 

 length, and the cell does not nearly extend to the base of the tentacula ; the 

 animal can be retracted, however, so as to he completely protectfd by the cell, 

 the edges of which are drawn in so as to close tlie aperture. The ctlls of the 

 Bowcrbankia are horny in their texture, and arise separately Irom a s(.irt ot 

 stolon or creeping stem, very much after the manner of the separate individuals 

 of the Poropfiora (see Appendix to MoUusca, Fig. 7): ii^ many other genera, 

 however, a solid calcareous labric is produced, in which the cells are imbedded ; 

 c^tunSiT^rf/onficx'.Ti'i- whilst in other instances, again, this fabric is soft in its texture, being sometimes 

 ^'^'■^^"'^' gelatinous as in the compound Ascidians, in other instances spongy as in the 



Alcyonian Pnlypes. 'i'he tentacala, of which there are ten in the Bowcrbankia^ but a greater 

 number in many other genera, are always furnished witli cilia ; by this character these animals are 



