424 LAWS OF MULTIPLICATION. 



Of animal aggregates belonging to the second order, that 

 multiply asexually with rapidity, the familiar Polypes 

 furnish conspicuous examples. By gemmation in most 

 cases, in other cases by fission, and in some cases by both, 

 the agamogenesis is carried on among these tribes. As 

 shown in Fig. 148, the budding of young ones from the 

 parent Hydra is carried on so actively, that before the oldest 

 of them is cast off half-a-dozen or more others have reached 

 various stages of growth ; and even while still attached, the 

 first-formed of the group have commenced budding out 

 from their sides a second generation of young ones. In the 

 Hydra tuba this gemmiparous multiplication is from time to 

 time interrupted by a transverse splitting-up of the body into 

 segments, which successively separate and swim away : the 

 result of the two processes being, that in the course of a 

 season there are produced from a single germ, great numbers 

 of young Medusa), which are the adult or sexual forms of the 

 species. Respecting Coelenterate animals of this degree of 

 composition, it may be added that when we ascend to the 

 larger kinds we find asexual genesis far less active. 

 Though comparisons are interfered with by differences of 

 structure and mode of life, yet the contrasts are too striking 

 to have their meanings much obscured. If, for instance, we 

 take a solitary Actinozoon and a solitary Ilydrozoon, we see 

 that the relatively- great bulk of the first, goes along with a 

 relatively- slow agamogenesis. The common Sea-anemones 

 are but occasionally observed to undergo self- division : their 

 numbers are not rapidly increased by this process. A 

 higher class of secondary aggregates exemplifies the same 



observed fixed to the glass "by a sheathed pedicle ; a ciliary motion became 

 perceptible at the top of the bulb ; and at ten it had divided longitudinally 

 into two buds, each supported by a short stalk. The ciliary motion continued 

 in the centre of each of these two buds, which by degrees expanded longitudi- 

 nally, and at twelve had become four buds. By four in the afternoon, these 

 four buds had divided in like manner and increased to nine, with an elongated 

 footstalk, and interior contractile muscle." 



