TJS Mr Huxley on a Species of ' Tubicolar Annelid. 



1. All the segments of the latter were segments of the 

 former, the new products being merely cephalic organs. 



2. None of the segments of the produced zooid belonged 

 to the parent zooid, but the former is a metamorphosis of a 

 whole segment of the latter. 



3. None of the segments of the produced zooid belonged to 

 the parent zooid, and the former contains hardly any of the 

 primitive substance of the latter, being developed by ger- 

 mination from its last segment. 



It is clear that the prolification of Protula Dysteri will come 

 under none of these categories ; but is a combination of the 

 first and second methods. The abdomen of the produced 

 zooid is a mere fissive product of the parent, but its thorax 

 is the result of the metamorphosis of a single segment of the 

 parent into many segments. 



Quatrefages endeavoured to show that the relation of the 

 produced zooids of Syllis to the anterior zooid was that of 

 an " alternation of generation,' 1 the former alone developing 

 sexual products. Krohn has however proved that no such 

 relation exists in this case ; but on the other hand he brings 

 forward good evidence to demonstrate that the posterior 

 zooids of Autolytus prolifer really are generative zooids, and 

 alone develop the reproductive elements. The male zooids 

 in this case are widely different from the gemmiparous zooid ; 

 so different, in fact, that they were regarded by 0. F. Muller 

 as belonging to a distinct species. 



I sought carefully for evidence of any such " alternation'* in 

 Protula Dysteri, but the result was to convince myself that 

 nothing of the kind exists. 



The generative products may indeed almost always be 

 detected, though the ova are very small and indistinct, in the 

 anterior zooid of any still unseparated pair ; and it is there- 

 fore clear that the gemmiparous zooid is not asexual, the in- 

 variable rule where that separation of the individual into 

 asexual and sexual zooids, which constitutes the so-called 

 " alternation of generations," really exists. 



