132 ANTHOZOA HYDROIDA. 



gestion, are again ejected by the mouth; but, as already mentioned, 

 the stomach is furnished with what, in one sense, may be called an 

 intestine, to which, according to Trembley and Baker, there is an 

 outlet in the centre of the base ; and the latter asserts that he has 

 " several times seen the dung of the polype in little round pellets 

 discharged at this outlet or anus."* 



But the Hydra is principally celebrated on account of its manner 

 of propagation. It is, like zoophytes in general, monoecious ; and 

 every individual possesses the faculty of continuing and multiplying 

 its race, principally, however, by the process of subdivision. During 

 the summer season, a small tubercle rises on the surface, which 

 lengthening and enlarging every hour, in a day or two develops in 

 irregular succession, or in successive pairs,t a series of tentacula, 

 and becomes, in all respects excepting size, similar to its parent. 

 It remains attached for some time, and grows and feeds, and con- 

 tracts and expands after the fashion of this parent, until it is at 

 length thrown off by a sort of sloughing or exfoliation. These buds 

 sprout, in the common species, from every part of the body inferior 

 to the stomach, but not from the tentacula ; and very often two, 

 three, or four young may be seen depending at one time from the 

 sides of the fruitful mother, in different stages of growth, each play- 

 ing its part independent of the others : 



" where some are in the bud, 



Some green, and rip'ning some, while others fall." 



They are evolved with rapidity in warm weather especially, one no 

 sooner dropping off than another begins to germinate ; " and what 

 is most extraordinary, the young ones themselves often breed others, 

 and those others sometimes push out a third or fourth generation 

 before the first fall off from the original parent." Trembley found, 

 in one experiment, that an individual of H. grisea produced forty- 

 five young in two months. The average number per month in 

 summer was twenty ; but as each of these began to produce four 



* Lib. s. cit. 27. He adds : " Much the greater and grosser part of what the 

 polype eats is most certainly thrown out again by the mouth, after lying a proper 

 time to become digested in the stomach : and, for a good while, I imagined there was 

 no other evacuation ; but am now convinced that the finer part, in small quantity, is 

 carried downwards through the tail, and passed off that way. I believe, however, 

 there is also another purpose to which this passage serves, and that is, to convey a 

 mucus or slimy matter to the end of the tail, for its more ready adhesion to sticks, 

 stalks, or other bodies." 



t Baker's Hist. 35. 



