CNIDARIA 71 



the Calycophoridffi are united into groups and sejiarated by intervals of 

 the stem {intey nodes). They bud in such a way that the group of indi- 

 viduals (cormidium) occurring at the lowermost end of the stem is the 

 oldest. In many cases (Polyphyidffi, Desmophyidaj, Praya, Galeolai'ia, 

 etc.) the groups of individuals, even if they produce sexual products, 

 remain united with the entire corm. In most of the Diphyidffi, on the 

 contrary, the oldest cormidia sejiarate from the parent stock before they 

 arrive at sexual maturity, and either as Eudoxia; or Ersffite lead an 

 independent life. In this way a kind of alternation of generations is 

 brought about, since the parent stock does not itself produce sexual 

 products, but separates into secondary stocks, which do not reach sexual 

 maturity until later on. Such a detached Eudoxia ivoup (so the 

 cormidia have usually been called) consists of a polypite with tentacles, 

 a hydrophillium, and a gonophore which develops the sexual products in 

 its manubrium, and at the same time by the rhythmical contractions of 

 its swimmmg sack produces the locomotion of the detached Eudoxia. 

 Haeckel explains the hydrophillium, the polypite, and the tentacles as 

 the constituent parts of a sterile person, in which the bilaterally 

 symmetrical hydrophillium would represent the umbrella of the medusa. 

 The Eudoxia cormidium would accordingly in the simplest case be 

 composed of two persons : a sterile one and a fertile one (the gonophore 

 or sexual bell). It is to be observed that the two persons named would 

 represent two essentially heteromorishous medusae of the same corm. 

 Whereas the sterile person exhibits a bilaterally symmetrical structure 

 and the above-mentioned dislocation of the parts, nothing of this kind 

 can be recognized in the fei'tile person. The structure here is that of an 

 ordinary quadriradial Anthomedusa, and the manubrium has retained its 

 usual place. 



Ledckakt and Gegenbaur have shown that in various Eudoxiae the 

 gonophore, after the discharge of its sexual products, is replaced by the 

 outgrowth of a new gonojjhore, and Chun showed it to be probable that 

 in all Eudoxiffi a quite regular replacement of the gonophores takes 

 place, so that each Eudoxia has quite a number of gonophores developed 

 one after another. Now let us imagine that the first one of these 

 gonophores remains sterile, functioning merely as an organ of locomo- 

 tion ; that would lead to the form of the Ersffiis (in Haeckel's sense). 

 As Ersaeae are designated the cormidia which bud on the stem of 

 Lilyopsis and Diphyopsis, and which, in addition to the parts described 

 for the Eudoxiffi, jjossess a so-called special swimming bell, so that 

 these cormidia, according to Haeckel's interpretation, embrace at least 

 three persons, two sterile and one fertile. 



The different parts of the nectosome are also subject to a quite similar 

 replacement by supervening buds. Even in the Diphyidae the two necto- 

 calyces are not retained throughout life. Leuckakt had already observed 

 the presence of two to three bud-like supplementary bells in Epibulia, and 

 Chun showed that the nectocalyces of the Diphyidae are subject to a con- 



