AVICULARIUM. 245 



These movements are sometimes so lively, that notwithstanding the 

 excessive minuteness of the Avicularia, the agitation of several at once, 

 proves very inconvenient for microscopical observation. Though nume- 

 rous on a specimen, not above one individual has been seen on any single 

 cell. In itself it is semitransparent. Farther than already described, no 

 subordinate parts have been detected. Whether they exist, must be in- 

 ferred from future discovery of its real nature. Meantime, we must allow 

 that much embarrassment attends all attempts to account for the presence 

 of these objects. Are they parasites affixed immovably to a certain spot ? 

 Are they an integral part of the zoopliyte ? What relation do they bear 

 to the cell or to the hydra ? Such points are of no easy solution. For a 

 long time, I was induced to conclude the Avicularium a parasite — for 

 there are animals, like the lepas or barnacle, and some other cirrhipedes, 

 whose parts are incorporated with wood, rocks, or shells. I cannot believe 

 that it is connected with the hydra, from finding it seated and active on 

 the side of those cells wherein there are none. Nevertheless, it is an in- 

 tegral part of the zoophyte, in so far as being generated along with new 

 or reproducing portions. This, indeed, does not exclude the character of 

 a parasite ; for I have undei-stood that those infesting the larger animals, 

 sometimes occur in the foetus. — PI. XL VIII. fig. 6. 



Without following the progress of the Avicularium, it could not be 

 recofnised from any resemblance between its earlier and later stages. At 

 first, it appears as a convex or hemispherical knob, crowning a cylinder. 

 While still farther advanced, it remains of imperfect form, triangular and 

 of light grey colour. Symmetry is afterwards attained. 



Many were regenerated or reproduced on portions of the Cellularia 

 fastigiata. 



A few remarks on a flexible organ sometimes issuing from the Ccllii- 

 Inria scruposa, are meantime reserved. 



Plate XLVI. Fig. 10. Avicularium, quiescent. 



1 1 . The same in activity ; basis, a ; head, b ; mandible open, c. 

 XLVIII. 6. Avicularium. 



These figures are enlarged. 



