484 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



it seems, to the injury done to the sponge by the 

 operation, no growth occurs during the first four 

 months, but during the next two months it will be 

 found to have grown two or three inches. 



Taking the groups in order, we find a higher grade 

 of localisation in the Ccelenterata than we should 

 have been led to expect from what we know of the 

 sponges. In Hydra, for example, the testes are 

 always placed just below the circle of tentacles, and 

 the ovary nearer the foot ; in the sea-anemone the 

 generative glands, or, as they may be more shortly 

 called, the gonads, are developed on the sides of the 

 primary septa ; in the jelly-fishes they are found on 

 the walls of the gastro-vascular canals. It is clear, 

 then, that there is localisation, but this is still of a 

 diffused nature \ the generative elements are not, as 

 in the crayfish or the fowl, limited to one aggrega- 

 tion, but there are several cell aggregates, each with 

 a reproductive function. 



This phenomenon is most striking in the case of a 

 colony of hydroid polyps, such as that presented by 

 Syncoryne. Here we find that, of the numerous 

 buds developed on the colony, some never attain 

 to nutrient functions, and never have the oral cone 

 or tentacles of a nutrient person (trophosome) ; 

 instead thereof, they become gradually fashioned into 

 the shape of bell-like Medusae, separate from the 

 colony, become free-swimming, and develop gonads 

 on the walls of their gastro-vascular canals. In other 

 cases the medusoid buds or gonosomes become 

 more or less completely developed, but never separate 

 themselves from the rest of the colony ; within such 

 buds gonads become developed. 



This method of division of labour, some persons 

 of the colony undertaking nutrient and others gene- 

 rative functions, is, as may be supposed, particularly 

 well seen in the Siphonophora, where special sets of 



