A FEW CCELENTERATES OF WOODS HOLL. 107 



devoid of definite perisarc. (This may be due in part to the 

 habitat, on the crab, these animals being given to decorating 

 themselves with various living organisms, such as hydroids, 

 polyzoa, algae, etc., and if this hydroid were there by such process 

 its very short stem devoid of perisarc may be due to its recent 

 transplantation.) The hydranth is 

 rather large, with two whorls of ten- 

 tacles, the basal series about twenty- 

 four in number, long, and filamentous, 

 much as in Tubularia ; oral tentacles 

 few and short, about ten or twelve, 

 apparently in two series, one very 

 short, merely bud-like. Hypostome 

 of hydranth rather cylindrical, entire 

 hydranth low vasiform, and with defi- Fig. 9. 



nite constriction below the body. 



Medusa-buds borne on body of hydranth in series of racemose 

 clusters, as shown in Fig. 9. Growth of medusas apparently 

 rapid, the older forming the terminal portion of the cluster 

 Color of hydranth pinkish red, tentacles paler. 



Medusa. — Bell transparent, subspherical or when older ob- 

 lately spheroidal ; diameter when first liberated about .5 to .6 mm., 

 and becoming but little larger after several days in the laboratory, 

 Walls of bell rather delicate, though not flabby ; velum very 

 delicate, with tendency to evert during contraction. Radial 

 canals four, rather open showing free movement of circulating 

 fluid. Tentacles four, rather short, and terminating in knob-like 

 masses of nematocysts, body of tentacles with nematocysts in 

 scattered clusters of four to six in number usually, though some 

 specimens seemed all but devoid of them. The entire exum- 

 brella of newly-born medusae is more or less dotted with clusters 

 of nematocysts. A characteristic feature of the medusa is the 

 presence of eight rows of nematocysts arching over the exum- 

 brella from the basal bulb of each tentacle, a row on either side. 

 Basal bulbs rather prominent, and with scattered granules of 

 pigment throughout their substance. Manubrium relatively large 

 or thick and not extending at any time to the level of the velum, 

 mouth devoid of lobes or lips of any sort. 



