SCYPHOZOA 155 



continued into them. The edge of the bell projects over them as a 

 hood. In each apical endoderm cell of the tentacle there is a crystal 

 which according to some authors is calcium oxalate. On one side of 

 the tentacle is a pigment spot which may be an ocellus, and near it are 

 two pits lined with sensory epithelium and said to be olfactory. In 

 the neighbourhood of these tentacles, then, all the senses appear to 

 be localized. Does this explain the fact that they are necessary for 

 the rhythmic contraction of the medusa bell } The Scyphomedusae 

 are excellent subjects for experiment, and if cut into ribbons will still 

 live and their muscles function. If the tentaculocysts are cut out one 

 by one the rhythmic movements of the bell continue until the last is 

 removed when they suddenly cease. After that, drastic stimulation, 

 tactile or chemical, is necessary to make the muscles contract. 



The gonads are situated, as has been already stated, in the floor of 

 the stomach, and the ripe gametes are liberated into the genital pouch. 

 The eggs are fertilized as soon as they become free by spermatozoa 

 from another individual which are drawn into the mouth along with 

 the food. They pass through the canals to the opening on the oral 

 arms (Fig. 129, o.o.fl.) and undergo the first stage of their development 

 enclosed in pouches at the side of the oral grooves. Little opaque 

 patches along the side of the lips are to be seen with a lens, and when 

 dissected out they prove to be masses of planula larvae. The planula 

 is eventually set free, but soon attaches itself to stone or weed and 

 develops into a small polyp, without perisarc, the hydratuba^ which 

 eventually grows sixteen long and slender tentacles. Internally this 

 stage has the same structure as Lucernaria with four interradial 

 mesenteries, which are invaded by vertical ectodermal pits, and form 

 perradial pouches between. At the base of the hydratuba a horizontal 

 stolon grows out, and off this fresh hydratubae may be budded. They 

 may separate from the parent as in Hydra. At certain seasons the 

 whole hydratuba is segmented by transverse horizontal furrows. This 

 process is termed strobilization (Fig. 130 B). In each of the disc-like 

 segments so produced, marginal growth at once begins, eight notched 

 lobes being formed, four of which are interradial and four perradial. 

 In each notch there is a short tentacle and this becomes a tentaculocyst. 

 Each lobe is provided also with two short lateral tentacles, but these 

 disappear. A prolongation of the gastric cavity into each lobe indicates 

 the beginning of the branched perradial and interradial canals, and at 

 a little later stage the ad radial canals also appear (Fig . 1 3 o D ) . The gastric 

 filaments are also seen as four pairs in the interradial mesenteries. 



The Scyphistoma is the name given to the segmented body and each 

 of the segments is an Ephyra larva (Figs. 127 D, 130). They lie upon 

 each other like a pile of saucers, connected, however, by strands of 

 tissue in which run the muscles of the interradial mesenteries con- 

 tinuous throughout the pile of individuals. These muscles contract 



