THE SIPHOXGPHORA. 131 



differentiated manubrium, and narrowing its cavity at differ- 

 ent points gives rise to the irregular canals (Fig. 27, Z>, d). 

 In the male gonophore the neciocalyx is more distinct from 

 the manubrium, and its extremity has a rounded aperture 

 (Fig. 27, E). 



In the Culycoplioridc^^ as in the elongated Fhysophoridce^ 

 the development of new hydranths and their appendages, 

 which is constantly occurring, takes place at that end of the 

 hydrosoma w^hich corresponds to the fixed extremity of one 

 of the Hydrophora y and, if we consider this to be the proxi- 

 mal end, new buds are developed on the proximal side of 

 those already formed. Moreover, these buds are formed on 

 one side only of the hydrosoma. Hence the appendages are 

 strictly unilateral, though they may change their position so 

 as eventually to appear bilateral or even whorled. In the 

 Cidycophoridce, the saccular proximal end of the coenosarc 

 (Fig. 22, A^ d) is inclosed within the anterior nectocalyx, at 

 the posterior end of w^hich is a chamber, the hydroecmm 

 (Fig. 22, A, c). The second, or posterior, nectocalyx is at- 

 tached in such a w^ay that its anterior end is inclosed within 

 the hydroecium of the anterior nectocalyx, while its contrac- 

 tile chamber lies on the opposite side of the axis to that on 

 which the anterior nectocalyx is placed (Fig. 22, A). Sets 

 of appendages (Fig. 22, A^ a ; Fig. 23), each consisting of a 

 hydrophyllium, a hydranth with its tentacle, and gonophores, 

 which last bud out from the pedicle of the hydranth — are 

 developed at regular intervals on the coenosarc, and the long 

 chain trails behind as the animal swims with a darting mo- 

 tion, caused by the simultaneous rhythmical contraction of 

 its nectocalyces, through the water (Fig. 22). 



From what has been said, it follows that the distal set of 

 appendages is the oldest, and, as they attain their full de- 

 velopment, each set becomes detached, as a free-swimming, 

 complex Dlphyzooid (Fig. 23). In this condition they grow 

 and alter their form and size so much, that they were for- 

 merly regarded as distinct genera of what were termed mono- 

 gastric Diphydm. The gonophores, with wiiich these are 

 provided, in their turn become detached, increase in size, 

 iDecome modified in form, and are set free as a third series 

 of independent zooids (Fig. 23, B). But their manubrium 

 does not develop a mouth and become a functional hydranth ; 

 on the contrary, the generative elements are developed in 

 its wall, and are set free by its dehiscence. 



In the Physophoridas, the proximal end of the hydrosoma 



