XVI 



UPON ANIMAL INDIVIDUALITY 



Proceedings of the Royal Institution, vol. i. 185 1-4//. 184-9 

 (Abstract of a "Friday Evening Discourse," April 30, 1852) 



The Lecturer first briefly described the structure of the Diphydse 

 and Physophorid^ — pointing out the general conformity of these 

 animals with the common Hydra. 



They differ, however, in this important respect ; that the body in 

 which the eggs are developed is in Hydra a simple process ; while in 

 the Diphydae and Physophoridse the corresponding body presents 

 every degree of complication from this form, to that of a free- 

 swimming, independent " Medusa." 



Still more striking phenomena were shown to be exhibited by the 

 Salpae. In this genus each species has two forms. In the example 

 chosen these forms were the S. democratica and the S. mucronata ; 

 the former is solitary and never produces ova, but developes a peculiar 

 process, the gemmiferous tube " ; upon which, and from which, the 

 associated Salpae mucronatse are formed by budding. 



Each of these carries a single ovum, from which the first form is 

 again developed. 



The Salpa mucronata, which is thus produced from the Salpa 

 democratica, is just as highly organized as the latter. It has as 

 complete a circulatory, nervous, and digestive apparatus, and moves 

 about and feeds as actively ; no one unacquainted with its history 

 would dream of its being other than a distinct individual animal, and 

 for such it has hitherto passed. 



But the Salpa mucronata has exactly the same relation to the 

 S. democratica that the free-medusiform egg-producing body of 

 Physalia or Velella has to the Physalia or Velella ; and this free- 

 medusiform body is homologous with the fixed medusiform body of 

 Diphyes ; which again is homologous with the semi-medusiform, 



