CLAVA SQUAMATA. 245 



contraction. Tt must not, therefore, be confounded with the capitula of Corijne, which arc not 

 only independent of the state of contraction, Ijut possess a structure different from that of the 

 rest of the tentacle. Heterocordyle Conyhearei and some other hydroids with filiform tentacles 

 show, like Clava squamata, a tendency to the terminal enlargement of the tentacles in certain 

 states of contraction. 



One of the most distinctive features of Chiva squamata is to be found in the peciUiar cceno- 

 sarcal expansion which forms a hydrorhiza, by means of which the whole cluster becomes united 

 into a compound colony, and rooted to the surface which supports it (fig. 1). 



Instead of being formed, as in the majority of IIvdroida, by a system of separate fililbrm 

 tubes, tlie component tubes of the hydrorhiza are here adnate along their sides, adhering to one 

 another by their very thin chitinous pcrisarc, so as to constitute a continuous expansion, which 

 is formed by sinuous anastomosing tubes, from whose free surface the rudimental stems, with the 

 little cup-like investment of perisarc, are given off at such short intervals that the hydranths 

 which they carry are closely crowded upon one another at their base. 



The chitinous tubes of the hydrorhiza and hydrocaulus have been described and figured by 

 Dr. Strethill Wright, in what he regards as two distinct species, and names Clava memhranacea 

 and Clava cornea} but which are both identical with the H^dra sq/iainata of Midler, the Clava 

 squamata of the present Monograph. The first, however, to draw attention to the fact that Clava 

 is not properly a naked hydroid, as had been previously asserted in descriptions of this genus, 

 was Leidy, who has shown" that an American species, which he names Clava multicornis, but 

 which Agassiz refers to his Clava leptostyla, is invested at its base by a distinct perisarcal tube. 

 A similar character is presented by all the other species of Clava. 



The development of the ovum in Clava squamata may be followed without much difficulty. 

 The female gonophores usually carry each a single ovum (figs. 3, G). I have occasionally met 

 with two ova in the gonophore, but never with more. The ciliated planula (figs. 7, 8) is of an 

 elongated club-shape and of a deep red colour. It is very contractile, and may sometimes be seen 

 stretched out in a straight line, sometimes more or less coiled on itself, occasionally to such an 

 extent that the two ends are brought into contact. After it has lost its cilia and become fixed 

 the first tentacles are produced in a verticil of four near the distal extremity (fig. 10). Imme- 

 diately below these, and alternating with them, another verticil of four tentacles is then deve- 

 loped, and then successive tentacles are thrown out behind those previously formed; but all trace 

 of any distinct verticillate arrangement soon becomes lost. 



In the mean time, short fleshy processes (fig. 11) — which afterwards multiply, ramifj^, and 

 coalesce, so as to form the hydrorhiza — extend themselves from the base of the young hydroid, and 

 from these new hydranths are budded forth, and thus give rise to the clustered colonies of the adult. 

 At a very early period — shortly after the appearance of the first tentacles — a very delicate struc- 

 tureless pellicle may be traced over the body of the hydranth, from its base almost to the roots 

 of the tentacles (fig. 11). During the life of the hydroid this continues upon its body as a 

 scarcely perceptible film, but at the base it becomes thickened by new layers, so as to con- 

 stitute the tubular perisarc of the hydrorhiza and of the rudimental hydrocaulus. 



1 Wright, in ' Proc. Roy. Phys. Soc. Ediub.,' 1857, p. 228, pi. xi, figs. 3, 4. 



" " ^Marine Invertebrate Fauna of Rhode Island and New Jersey," iu ' Journal of Acad. Nat. Sc. 

 of Philadelphia,' vol. iii, second series, 1855, pi. ii, figs. 33, 34. 



