FHE BRYOZOA BASSLER. 



373 



on a slide and after heating to harden the balsam rubbing it gently 

 on a soft hone. 



Avicularia and vibracula. — The " bird's head " organ or avicu- 

 larium (text fig. 15) attached to the zooecia of many Cheilostomata 

 consists of a small cell containing a rudimentary polypide and of a 



large avicularia pre- 

 are small and devel- 



Fig. 15. — Avicularia ami Vibracula 



1. Holoporvlla descostilsii Savigny-Audouin, X 25, with 

 serving bar on which the mandible operates. 



2. Antropora granulifcra Ilincks, X 30. The avicularia 

 oped in pairs just above the aperture. 



3. QrammeUa crassimurginata Hineks, X30, in which the avicularia are yery 

 similar to the zooecia but may be distinguished by the occurrence of the bar. 



4. Mastigcphora hyiiihiuinni Johnston, X 30. Zooecia preserving the long vi- 

 braculum and the pore from which it emerges. (After Hineks.) 



mobile chitinous mandible which in life keeps up a snapping motion. 

 The latter peculiarity led to the belief that the purpose of the avicu- 

 laria was one of defense, but it is more probable that they have some- 

 thing to do with alimentation or oxygenation. The mandibles are 

 symmetrical objects corresponding to the opercula of normal zooecia 



Various types of this chitinous portion of the avicularium,, magnified, which 

 is useful in the identification of cheilostomatous bryozoa. 1, Adeoncllop- 

 sis; 2, Smittina; 3, Pcristomella ; 4, ScMzopodrclla ; 5, Smittma; 6, Rete- 

 poraj 7, Holoporella ; 8, Retepora; !), Adeona; 10, Triphyllozoon ; 11, Thal- 

 amoporeUa ; 12, Smittina; 13, U»iJjonulaj 14, Thalamoporetla. 



and like them varying in shape with the species, so that the determi- 

 nation of their size and shape is as essential in detailed work as that 

 of the opercula. Their preparation for study under the microscope 

 is the same as for the opercula, already described ; indeed, the two 

 will almost always be found on the same slide. Some of the varia- 

 tions in the form of the mandibles are illustrated in text figure 16. 



