72 EMBRYOLOGY 



stant replacement by reserve nectocalyces of the same form. This 

 replacement also plays a considerable role, as we shall see directly, 

 in the metamorphosis of the Calycophoridie. 



The metamorphosis of the Caljcophoridte has been m.ade 

 known chietlj through the investigations of Chun (No. 54). 

 These refer principally to the development of the Mono- 

 phyidse, i.e. those forms which are characterized by the 

 possession of a single nectocalyx on the nectosome. In a 

 small Monopliyid called by Chun Muggiaea Kochii, and 

 characterized by its tall pentagonal nectocalyx, Chun was 

 able to prove that the larvoe arising from the eggs at first 

 possess a quite differently shaped, cap-like nectocalyx. By 

 the casting off of this primary provisional nectocalyx and 

 its replacement by the permanent heteroraorphous one, 

 these larvae, designated as Monophyes primoi'dialis, pass into 

 the Muggiaja form, from the stem of which the groups of 

 individuals at sexual maturity detach themselves as Eudoxia 

 Eschscholtzii. 



Since Chun has recently been able to prove the presence 

 of these primary, heteromorphovis, deciduous nectocalyces 

 in the case of the Polyphyidae, it may be considered probable 

 that such nectocalyces also belong to the larval stages of all 

 CalycophoridfB. According to Chun's theory, which Haeckel 

 has adopted, the fundament of the pneumatophore in the 

 PhysophoridjB would be homologous to the deciduous, pri- 

 mary nectocalyx of the Calycophorida?. 



General Considerations. — As regards the derivation of 

 the Siphonophora, there are at present two views, as yet 

 directly opposed to each other, undei'lying both of which is 

 the conception that the Siphonophore is a polymorphous 

 animal stock that has arisen by budding. But while some 

 authors (Leuckart, Claus, Chun) assume the starting-point 

 of this stock to be a floating hydroid-polyp stocklet, which 

 already had the power of producing medusae {hydroid theory), 

 others (Balfouk, Haeckel) derive the Siphonophore from a 

 medusa, which, by the budding of its manubrium (like Sai'sia 

 or Hybocodon), was able to produce new medusas {medusa 

 theory). Tlie former authors accordingly have two funda- 

 mental forms from which they are able to derive the mani- 



