298 



MEDUSA OF THE WORLD. 



of the pear-shaped planula. This narrow end afterwards becomes invaginated; the invag- 

 inated cells are, however, ectodermal, and have nothing to do with the gastrula cavity, but 

 they form the cement gland which soon serves to attach the larva. One lip of this orifice of 

 invagination grows faster than the other, so that the cavity is soon pushed to one side and 

 the larva becomes bilateral. When the larva attaches itself this invaginated ectoderm is pro- 

 truded and pours out its cement. The planula then elongates and forms a layer of perisarc 

 which fastens it throughout its entire length. It thus becomes a hydrorhiza, not a hydranth. 

 The first hydranth buds out at right angles to the length of the hydrorhiza at the end opposite 

 to the cement gland. As soon as the first hydranth has acquired mouth and tentacles another 

 buds out close to the base of the first and so on. The planula, therefore, persists as a root 

 (hydrorhiza) and produces the hydranths by budding. 



Fig. 161. — Larva of Eutima mira, after Brooks, in Mem. Boston Soc. Nat. Hist., vol. 3. 



The young hydranth has a tentacular basal web and 5 large alternating with 5 smaller 

 tentacles; io in all. The body of the hydranth is elongated and cylindrical, and is not covered 

 by the perisarc which invests the unannulated stem. The hydroid is a Campanopsis, very 

 similar to that trom which Claus, 188 1, reared Eutima [Octorchis] gegenhauri. 



Eutima cuculata Brooks. 



Eutima cuciihita, Brooks, 1883, Studies Johns Hopkins Univ. Biol. Lab., vol. 2, p. 140. 



Bell about 8 mm. in diameter and quite flat, being about 4 times as wide as high. The 

 gelatinous substance is quite thick in the center, so that the cavity of the bell is very shallow 

 and forms less than halt ot the total height of the bell. The gelatinous substance diminishes 

 gradually in thickness from the center of the margin, where it forms a thin edge. 4 slender 

 tentacles, which are 3 or 4 times as long as bell-diameter. The basal bulbs of these tentacles 

 are small and there are no lateral cirri. Above the base of each tentacle is a small semi- 

 circular flap or hood, which is formed from the gelatinous substance of the bell. There are 9 

 or 10 very small marginal cirri in each quadrant. There are 8 lithocysts, 2 in each quadrant. 



