238 THE MICROSCOPE. 



the animals live, and from worse foes. From this mode of connection 

 it results, that when the animals retire within, they at the same time 

 must close the aperture to their cells ; for that portion of the inner 

 tunic which is pushed outwards by their exit, in their withdrawal 

 follows the body by a process of invagination, becoming at one and the 

 same time a sheath for the column of tentacles, and a plug to the aper- 

 ture, which, when of a flexible material, has its margins also drawn 

 tighter and closer together." 



The cells are of various shapes, and from one, grow into a family 

 of millions, budding forth from the sides ; and though the living matter 

 disappears, the catacombs exist for the foundation of their families, 

 branching out and enduring for ages. 



Bryozoon Bowerbankia received its name from Dr. Arthur Farre, 

 in honour of the well-known microscopist, Mr. Bowerbank. A mag- 

 nified representation of the animal is seen in the frontispiece, Plate 

 I. No. 1. 



Dr. Farre gives the following description of Bowerbankia densa: 

 " When fully expanded, it is about one-twelfth of an inch in length. 

 In its retracted state, it is completely enclosed in a delicate horny cell, 

 sufficiently transparent to admit of the whole structure of the contained 

 animal being seen through its walls. The cells are connected together 

 by a cylindrical creeping stem, upon which they are thickly set, sessile, 

 ascending from its sides and upper surface. The animal, when com- 

 pletely expanded, is seen to possess ten arms of about one-third the 

 length of the whole body ; and each arm being thickly ciliated on either 

 side, and armed at the back by about a dozen fine hair-like processes, 

 which project at nearly right angles from the tentacles, remaining 

 motionless, while the cilia are in constant and active vibration." 



Notamia, or Back-cell, so named from the cells being exactly oppo- 

 site, and united back to back with a thick partition, and having a joint 

 above and below each pair. 



In some species of the Flustrce the interior of the cell is protected 

 by a lid which bears some appearance to the head and beak of a bird, 

 and hence it is termed the bird's-head process. This has long been 

 a subject of investigation by naturalists : George Busk, Esq., F.E.S.* 

 contributed to the Transactions of the Microscopical Society 1849 an 

 admirable paper on the Notamia busaria, or Shepherd' s-purse Coral- 

 line (represented in fig. 107, Nos. 1 and 3), which adds to our know- 



* Mr. Busk Las added much to the description here given of this bird's-head pro- 

 cess in the Quarterly Journal of Microscopical Science for January 1854. 



