CALYCONECTAB. 



147 



in which case a special nectocalyx is developed as a swimming organ. 

 The gonophores are of separate sexes, but the same stem is usually 

 hermaphrodite, bear- 



ing male and female 

 cormidia. 



The variations in 

 structure of the order 

 depend principally 

 upon the number of 

 the nectocalyces. In 

 the Monopliyidae 

 there is one necto- 

 calyx, in the Diphyi- 

 dae two, and in the 

 Polypli yi< hie several 

 pairs of nectocalyces. 



The first formed 

 mouthless siphon is 

 supposed by Haeckel to 

 elongate and form the 

 stem of the future colony. 

 The oldest cormidium is 

 that which is placed 

 furthest from the necto- 

 calyces (Fig. 122). Chun 

 states that the first nec- 

 tocalyx (cap-shaped) is 

 retained only in Mono- 

 phyes and Sphacroncctcs 

 (Fig. 121) ; in the other 

 Calyconectac it is thrown 

 off and replaced by a 

 differently shaped (pyra- 

 midal) secondary necto- 

 calyx (Fig. 122), to 

 which more secondary 

 nectocalyces are added 

 later. All Calyconectae 

 pass therefore through a 

 monophyid stage. 



As stated above the 

 buds of the cormidia are 

 always formed at the 

 upper end of the stem, 

 so that the oldest cor- 



A 



-c.oL 



-sn 



tr 



FIG. 122. Young colony of Muggiaea Tcochii with the primary 

 cap -shaped nectocalyx (A) which is soon cast oft', and 

 the secondary pyramidal nectocalyx (B). c.ol somatocyst 

 with oil-drop; hy hydroecium ; tr coenosome (stem) with 

 two cormidia, the upper one being the younger ; Br bud 

 of hydrophyllium ; go bud of gonopliore ; p siphon ; t 

 tentacle, su sub-umbrella. 



midium is the lowest (Fig. 122). The law as to the formation of the necto- 

 calyces is not clear in the Calyconectac, but in the Pkysonectae the pneumatophore 



