Rev. T. Hincks on the Folijzoan AvicuJarium. 21 



zooecium with its contained zooicT has been amply demon- 

 strated and is now generally admitted. Indeed the rudimen- 

 tary or primary forms of the organ exhibit so slight an amount 

 of divergence from the ordinary cells, that we have no diffi- 

 culty in recognizing the morphological relationship between 

 the two ; and from this starting-point a ^ries of transitional 

 forms conducts us to the most highly specialized term, in 

 which the zooecial type is effectually masked. The true 

 " l)ird's-head," with its elaborate prehensile apparatus, its 

 delicate tactile organ, and its half-rhythmical movement, is 

 confined to a few genera ; but between it and the earliest 

 stao-e of the transformation (a slight modification of the oral 

 valve) is interposed a multitude of forms, exhibiting a wonder- 

 ful variety of structure, and discharging the important func- 

 tion of defence in many diverse ways. The morphological 

 line which leads up to the articulated and movable " bird's- 

 head " is flanked by a host of branch lines, in which the 

 development assumes many directions and culminates in very 

 different structures. In a large proportion of these structures 

 the prehensile faculty is very feebly manifested, if at all. The 

 mandibular portion, which is the representative of the oral 

 valve of the cell, is little fitted to seize intruders or to hold 

 them in its grasp. In very many cases the hooked extremity, 

 which distinguishes the " bird's-head " is altogether absent ; 

 the mandible is rounded or spatulate, and works more like the 

 lid of a box than as a seizing-organ. In such cases the de- 

 fensive action must be limited, it would seem, to the opening 

 and closing of the mandible, which may have a deterrent 

 effect on unwelcome visitors. As the appendages are often 

 developed in immense numbers over the colony, it is quite 

 conceivable that the safety and comfort of the polypides may 

 be largely promoted by their movements. 



On the other hand, where only a single avicularium is pre- 

 sent (as often happens), or the size is very diminutive, and 

 the action of the mandible proportionately feeble and incon- 

 spicuous, it is difficult to understand what useful office it can 

 discharge. 



In a considerable number of cases the mandible assumes a 

 form wliich is still less compatible with any prehensile func- 

 tion. The pointed extremity is more or less elongated into a 

 spine-like process, which projects beyond the fixed beak on 

 which the movable jaw works. In some species (e. g. Schizo- 

 j)orella vulgaris^ Moll) this modification is carried to a great 

 extent, and the result is a long and slender setiforni appendage, 

 which may help, as it sways to and fro, to keep off creatures 

 or substances that would be injurious to the polypidc. Occa- 



