HYDROZOA CRASPEDOTA. 767 



Lendenfeld, Z. A. vi. p. 70). The notochord-like axial cells of the tentacles (p. 

 329) often become irregularly arranged in the adult, and they are in many instances 

 united by a basal ring of similar cells, e. g. in Tubularia, Eucopella. Other 

 elements are epithelio-muscle cells, the processes of which take as a rule a circular 

 direction, absent in Campanularidae and Sertularidae^ except in the hypostome, e. g. 

 of Eucopella (Pothers); of glandular absorbent and excretory cells, cf. von Lenden- 

 feld, Z. W. Z. xxxviii. pp. 522-5. Whenever muscle cells are well developed, the 

 endoderm is thrown into prominent longitudinal rugae, at least in the contracted 

 state of the hydranth. These rugae are more feeble in other instances. 



The ambulatory medusae Clavatella and Eleutheria (see note 4, p. 759) have 

 branched tentacles. The basal or first branch ends in Clavatella in a sucker, or in- 

 Eleutheria in a knob laden with cnidoblasts. The swimming form Cladonema has 

 three similar adhesive processes to each tentacle, and Hincks has observed it 

 reverse its bell and adhere by the processes in question while fishing for food with 

 the manubrium (A. N. H. (4), x. 1872, p. 392 *). The reversion and atrophy of the 

 bell when the sexual products are ripe has also been observed in some instances, 

 e. g. Cladonema (Allman, Gymnoblastic Hydroids, p. 359 ; Hincks, British 

 Hydroid Zoophytes, i. p. xxviii.). Solid tentacles, i. e. with an endodermal axis, 

 occur in some Leptomedusae, e. g. in Obelia. The exumbrellar ridges of Eucopella 

 have been examined by von Lendenfeld, who finds that they consist of a meridional 

 nerve with ganglion cells, young cnidoblast cells, and an overlying epithelium of 

 cnidoblasts and sense cells. The otocyst in the same medusa is connected to both 

 nerve-rings, and contains a basal ganglion. 



The sexual products originate from interstitial ectoderm cells in many medusae 

 after they are detached, or even before, e. g. Perigonimus. In some species of 

 Obelia they migrate from their place of origin at the base of the manubrium to the 

 radial canals (Hartlaub). The ova pass into the endoderm, wander through it, and 

 ripen partly in the endoderm, partly in the ectoderm of the radial canals. The 

 male cells, however, ripen exclusively in the ectoderm. The ova of the medusa of 

 Podocoryne originate in the gonophore-bud. 



With the degeneration in development of the sexual zooid (p. 762, ante) the 

 place in which the sexual cells first originate is altered. They may arise in the 

 entocodon, e. g. in Tubularia (2), male Clava (3), Pennaria (i) 2 ; in the endoderm 

 of the gonophoral bud, e.g. Coryne (3); or in the coenosarc, but in different 

 positions, e. g. at the place of origin of the gonophore itself, Hydractinia (3), male 

 Cordylophora (5), female Clava (3), in the budding zone of the hydranth, from the 

 hydrocope of which the blastostyle buds, male Eudendrium racemosum (3), 

 Gonothyrea (i), Campanularia (female 4, male 5), or in a budding zone of a 

 principal hydranth of the stem, female Cordylophora (5), zn.& Eudendrium (5). They 

 sometimes originate in the hydrorhiza, as in Eudendrium capillare (5) and Eucopella 

 (i). The sexual cells themselves in these cases are very commonly cells of the 

 ectoderm, and they may migrate in it from one spot to another, e. g. female 

 Cordylophora^ male Campanularia flexuosa. They may pass into the endoderm, 



1 A partial reversion has been noted by Allman in a Medusa, Circe invertens, Nature, ix. p. 74 ; 

 see p. 760, and note p. 751. 



2 The numbers in brackets correspond to the numbers affixed to the paragraphs on p. 762, and 

 how what stage of degeneration the sexual zooid has reached. 



