94 



co:mpaeative anatomy. 



the products of wliich are developed in tliem in tlie same manner 

 as are those of the free Medusfe. 



With these are connected still simpler forms of buds^ and the 

 series ends with buds the structure of which has scarcely anything 

 in common with a Medusa. But the series which leads to these 

 is perfect, owing to numerous intermediate forms, so that external 

 buds, merely containing generative products, and Medusee of a rela- 

 tively high organisation, which only become sexually mature some 



time after leaving the Hydroid 

 stock, must be regarded as the 

 widely-separate terminalpoints 

 of one series. 



This phaenomenon is ex- 

 plained by the conception of a 

 division of labour, in which 

 the function of feeding the 

 stock falls to the share of the 

 individuals which remain ses- 

 sile, while others which are 

 broken off take on the duty 

 of sexual reproduction. Those 

 buds which will become free 

 have a higher organisation, 

 which has been gradually de- 

 veloped from the lower forms, 

 and primitively resembled 

 those that remain sessile. The 

 separation from the stock may 

 therefore be regarded as the 

 primary cause of the differen- 

 tiation of the sexual individuals 

 in the medusoid direction, 

 while the permanence of the 

 sessile habit of the medusoid 

 buds, in other cases, is accom- 

 panied by a degeneration of 

 their medusoid organisation. 

 But if this organisation, as we supposed above, has been obtained 

 by a primitive freedom of life, the medusoid buds must necessarily 

 be regarded not as arrested in an onward development, but rather 

 as Medusa-buds in course of degeneration. A definite conclusion 

 on the subject is not possible, on account of the fact that the several 

 stages of degeneration might be precisely similar to those of deve- 

 lopment, and retrogressive metamorphoses have not been directly 

 observed. 



The gemmation of generative individuals, for such must the 

 medusiform buds and then' modifications be considered to be, takes 

 place at different points. As the formation of a stock is a secondary 

 process, the production of buds on the body of the single animalmustbe 



Fig. 32. A portion of a colony of a Hydroicl- 

 Polyp (Eudendrium ramosum) with bud- 

 ding MedusEe. jj p p Nutritive persons. 

 ahcdef Different stages in the diiferen- 

 tiation of the budding MedusEe. m m Free 

 Medusce in different positions. 



