OF ZOOIDS IN THE HYDROIDA. 



105 



a centripetal order of development, thus giving us, according as the buds are 

 sessile or pedunculated, the true spike, or the true raceme. 



The reversed spike, or spike with a centrifugal development, shows itself in 

 such forms as Dicoryne conferta (fig. 2, be); while in Campanularia (fig. 3), 

 Laomedea (fig. 4, b b'), Obelia, and other calyptoblastic forms, we have a reversed 

 spike surrounded by the gonangial sheath ; and were it not for the centrifugal 

 development of the generative buds upon the blastostyle, and the complete 

 closure of the gonangium, strongly recalling the spadix with its spathe in the 

 inflorescence of an araceous plant. 



In Eudendrium the male gonophores are disposed in an umbel (fig. 7, b) with 

 the axis, in some cases prolonged beyond it, while in others there is little or 

 no extension of the axis beyond the depressed portion which carries the gono- 

 phores. Though we cannot here recognise any difference in the order of 

 development among the gonophores composing the umbel, we are justified 

 in assuming this order to be as in the true umbel — a centripetal one ; for in the 

 female colonies of most species of this genus, such as Eudendrium ramosum, 



Fig. 8. Fig. 9. 



A blastostyle of Sydractmia, carrying its gono- A hydranth of Clava with its gonophores surround- 



phores, which increase in maturity toward s lie ing it in globular clusters. 

 proximal or attached end. 



the gonophores are separated from distance to distance upon the stem imme- 

 diately below the hydranth ; and here their order of development is plainly seen 

 to be centripetal. 



In Hydractinia echinata (fig. 8) we have the closely approximated gonophores 

 sessile on a blastostyle, and the development centripetal, as in the true spike, 

 while the axis extends beyond it as a naked prolongation, reminding us of the 

 naked prolongation of the spadix in certain Aracece. 



In Clava sqicamata, and in Clava multicornis, the gonophores form dense 



VOL. XXVI. PART I. 2 E 



