HTDROIDS FEOM WOOD's fiOLL, MASS. 355 



ing a coarse network. The polyps generally arise singly from 

 the hydrorhizaj and do not branch. While the hydrorhiza is 

 covered with a delicate perisarc, I could not demonstrate it 

 with certainty on any part of the polyps, and so cannot verify 

 Allman's prediction that a rudimentary hydrocaulus will be 

 found in Corynitis.^ 



As a rule the polyps are slender club-shaped bodies, from 

 1^ to 2 mm. in length (fig. 12). There is no marked division 

 into hydranth and hydrocaulus, as Agassiz has pointed out, 

 except that the proximal third is free from tentacles. The 

 oral end is quite blunt, but the hypostome as well as the 

 body is flexible and contractile. Distally the polyp is beset 

 by from thirty to forty-five short knobbed tentacles, which are 

 not arranged in regular circles, but in somewhat oblique rows, 

 giving rise to the spiral arrangement described by Agassiz. 

 The longest tentacles are not more than yL. mm. in length, 

 being nearest the oral end, while the aboral ones are repre- 

 sented by mere elevations on the body. The upper tentacles 

 do not form a circlet around the hypostome, there being a 

 single one higher than the rest. The longer tentacles bear 

 definite large nettling knobs at their ends; a solid row of 

 endoderm cells forms their axes. Nettling organs are also 

 found in the ectoderm of the body migrating^ toward the 

 tentacles from the base of the polyp where they are developed. 

 Medusa buds appear most numerous in a zone where the 

 rudimentary tentacles are, though scattered ones may also be 



^ This summer I have found what appears to be a second species of Cory- 

 nitis. It differs from C. Agassizii in the presence of a well-developed peri- 

 sarc on the hydrorhiza and the short hydrocaulus, forming imperfectly 

 annulated cups about one fourth the length of the polyp, and in the fact that 

 the medusa-buds are on branched stalks. The colony was not in good enough 

 condition to be sketched, and no medusae were freed, so it must be left for 

 future observation to determine its relationship. 



2 In a recent article, ' Biol. Centralblatt,' Bd. xvii, No. 13, 1897, v. Len- 

 denfeld has thrown doubt on the fact of the migration of nettling organs. In 

 this connection it is sufficient to state that for several summers in succession 

 this phenomenon has been observed on fresh Pennaria by our students in the 

 laboratory here. 



