442 Eepoet of the State G-eologist. 



fissa. (II.) The resemblance in minute detail between the avi- 

 cularian cell and the species to which it belongs, which are not 

 unfrequently met with, have a like significance. Thus, to take a 

 single illustration, in one species a minute sinus occurs on the 

 lower margin of the avicularian mouth, corresponding with a 

 similar sinus in the orifice of the zooecium. Instances of the 

 same kind might be multiplied. The function of the avicularia 

 is difiicult to determine ; nor indeed can the same function be 

 assigned to all of them. The primary forms are many of them 

 quite unfit for prehensile work. The lid-like mandible, with 

 plain rounded margin, has no power of grasping and could not 

 detain for a second the active worms which are sometimes cap- 

 tured by the articulated kinds. Their service for the colony 

 must lie in some other direction. Even the fixed transitional 

 forms, in which the beak and curved mandible are present, must 

 be ineflBLcient for this work from their want of mobility, whilst in 

 many of them the parts concerned in the act of prehension are 

 but slightly developed. The articulated avicularia are, however, 

 undoubtedly grasping organs, and the presence of the tactile 

 tuft between the jaws must be taken to indicate that capture in 

 some form or other is their function. They have been seen to 

 arrest minute worms and hold them for a considerable time with 

 a tenacious grip as if with some ulterior object, but what the 

 object may be, it is difiicult to decide. Dr. Johnston suggested 

 that they may assist in providing supplies of food, seizing ' cir- 

 <3umfluent animalcules,' and retaining them until, enfeebled or 

 killed by the grasp, the ciliary currents may bear them to the 

 mouth. But the avicularium is not fitted to capture the ex- 

 tremely minute organisms in which the polypides feed ; and even 

 if they could be captured and rendered helpless, there would be 

 many chances, placed as the appendages usually are, against 

 their coming within the attraction of the ciliary vortex. The 

 worms, which seem to be the commonest victims, could only be 

 utilized as food by being retained until decomposition having set 

 in, the particles of decayed matter might diffuse themselves 

 through the surrounding water and find their way, in a greater 

 or less degree, to the stomach of the polypides. But the sup- 

 plies of nutriment in the waters of the ocean must be ample and 

 unfailing, and no better provision for appropriating them than 



