GROWTH OF POLYPIDOM. 95 



mass, or occasionally it may be seen so completely contracted as simply 

 to form a broad lip-like ring around the oral opening. 



(224.) The stomach, as in the Hydra, is a simple cavity excavated 

 in the interior of the body, without any proper parietes, which inferiorly 

 communicates immediately with the fleshy substance contained in the 

 common polypary ; so that the contents of the stomachal sac may not 

 unfrequently be seen to pass into the living pith, and in like manner 

 the globules there circulating to return into the stomach. 



(225.) The multiplication of these beautiful zoophytes appears to 

 take place in three different modes : 1st, by cuttings, as in plants ; 

 2ndly, by offshoots, or the formation of new branches bearing polyps ; 

 3rdly, by Planulce capable of locomotion. 



(226.) The first mode strikingly resembles what is observed in the 

 vegetable kingdom ; for, as every branch of the plant-like body contains 

 all the parts necessary to independent existence, it can hardly be a 

 matter of surprise that any portion, separated from the rest, will con- 

 tinue to grow and perform the functions of the entire animal. 



(227.) The second mode of increase, namely, by the formation of new 

 branches and polyps, seems more like the growth of a plant than the 

 development of an animal. We will consider it under two points of 

 view : first, as regards the elongation of the stem ; secondly, as relates 

 to the formation of fresh cells containing the nutritive polyps. On ex- 

 amining any growing branch, it will be found to be soft and open at the 

 extremity, and the soft tegumentary membrane (above described as 

 forming the tube by its conversion into hard substance) is seen to pro- 

 trude through the terminal orifice ; the skeleton is therefore not merely 

 secreted by the enclosed living granular matter, but it is the investing 

 membrane, which continually shoots upwards, and deposits hard material 

 in its substance as it assumes the form and spreads into the ramifica- 

 tions peculiar to its species. 



(228.) Having thus lengthened the stem to a certain distance, the 

 next step is the formation of a cell and a new polyp, which is accomplished 

 in the following manner*. The newly-formed branch has at first pre- 

 cisely the appearance and structure of the rest of the stalk of the zoo- 

 phyte (fig. 46, 1), being filled with granular matter, and exhibiting in 

 its interior the circulation of globules (already described) moving to- 

 wards the extremity along the sides of the tube, and in an opposite 

 course in the middle ; the end of the branch, however, before soft and 

 rounded, soon becomes perceptibly dilated. After a few hours the branch 

 is visibly longer, its extremity more swollen, and the living pith is seen 

 to have partially separated itself from the sides of the tube, the bounda- 

 ries of which become more defined and undulating (2). The growth 

 still proceeding, the extremity is distinctly dilated into a cell, in which 

 the soft substance seems to be swollen out, so as to give a rude outline 

 * Lister, Phil. Trans, loc. cit. 



