30 NATURAL HISTORY OF 



different parts of the colony. In the Thecapltora they 

 are always produced from the coenosarc, and protected 

 by a chitinous gonotheca or capsule. In the Athecata 

 they are not protected, and arise from various portions, 

 in some species of the coenosarc, in others of the 

 polypite. The gonophores consist of an outer covering 

 or perigonmm and the contained gonozooid. The 

 gonozooids are either fixed or free. Those that are 

 fixed discharge their contents, whether ova or sperm 

 cells, on the spot. 



The free gonozooids, on the other hand, at a certain 

 stage break out of the gonophore, and enter upon a 

 separate existence as medusiform zooids (see Plate I. 

 fig. 6). The form of this free gono^iooid is that of an 

 umbrella or swimming-bell (a), which by its constant 

 systole and diastole floats about in the water. From 

 the centre of the bell hangs a manubrium [m), which 

 is hollow and terminates in a mouth. At the end 

 opposite to the mouth it joins four tubes (c) which 

 extend to the margin of the umbrella, and there 

 pour their contents into a small channel (/) which 

 runs round the bell. The bell is partly closed at the 

 bottom^ by a vehim or veil, which is perforated in the 

 centre (e) to admit of the passage of food to the mouth. 

 The margin of the bell is furnished with tentacles, at 

 the base of which are developed often eye-like spots 

 (ocelli) which are believed to serve the purposes of 

 vision. They are, however, very rudimentary organs. 

 The medusiform zooid is capable of reproducing 

 its own form by gemmation, just as the ordinary 

 hydra, but ultimately the elements of reproduction are 

 developed in the neighbourhood of the manubrium. 

 When these elements are ready for dispersion, the 



