BY DR. R. VON LENDENFELD. 209 



In the simplest case of Protohydra we have a Polype, which 

 multiplies by fission and is propagated by generative elements, 

 produced in the wall of the body. Hydra multiplies by budding 

 and also produces ova and Spermatozoa in the wall of the gastral 

 cavity. 



Both these Hydroids always remain single and never form 

 colonies : the budding persons are always completely isolated from 

 the parent. The same thing happens in the case of Myriothela. 



In the stock-forming Hydroida, most of the buds do not attain 

 personal liberty but remain in connection with the primary 

 Polype, their common parent, by tubes through which the nutritive 

 chymus fiows freely. In the simplest case all the Polypes 

 belonging to one colony are alike : Clava is to be compared to a 

 colony of Hydra's. Whilst in Clava and Tabiclava the generative 

 elements are produced by all the Zooids, in other Hydroids the 

 production of generative elements devolves on certain Zoids only, 

 which change their shapes and became Blastostyles ; whilst the 

 other Zooids remain pretty much unchanged in appearance, losing 

 only the I'eproductive faculty. Division of labour causes some 

 persons belonging to the stock — a simple political unity — to 

 become alimentary, and others to attain reproductive functions. 



To this group belong the Cordylophorinse, Binierinee, Campan- 

 larinse, Sertularinas, and perhaps also the fossil Graptolithes. Also, 

 the Pluinulavidaj are placed in it. 



The Plumularidaa are characterized by the tranformation of 

 some of the Zooids into Machopolypes. These are persons whose 

 main duty is to defend the stock against outer enemies, and to 

 attack, slay, and bring home, food for the nutritive Zooids. They 

 are the soldiers and fishers of the colony ; often as many as 80% of 

 the Zooids of a colony are thus transformed into soldiers, a state of 

 affairs not even reached by the Continental powers. These 

 Machopolyps, or rather the cups in which they live, were formally 

 called Neuiatothecae or Sarcothecse. 



