662 MEDUS-E OF THE WORLD. 



The young larvse are set free from the mouths of the mother medusa as planulae or young 

 gastrulje. Segmentation is total and nearly equal. The gastrula is formed by invagination 

 as in the case oi Aurellia. The free-swimming planula is pyriform to oval, flattened laterally, 

 and ciliated externally. The entoderm of the planula is entirely encased by the ectoderm 

 through the closure of the blastopore, and thus the planula is a two-layered sac which attaches 

 itself to the bottom b\ means of its broad anterior end, and then loses its cilia. 



An invagination of the ectoderm takes place at the posterior (now uppermost) end of the 

 planula. According to Goetie the entoderm is also evaginated at the same time in such manner 

 that two backwardly projecting pouches remain in the plane of the wide lateral diameter, 

 while these pouches are absent on the flat sides of the larva. The ectodermal invagination 

 forms the mt)uth and o-sophagus; while the entodermal evaginations torm the first pan ot 

 lateral stomach-pouches. .\n opening is soon formed where the invaginated ectoderm has 

 fused with the entoderm, and thus the throat-tube is placed in communication with the central 

 stomach. The second pair of gastric pouches now arise 90° apart from the first and, according 

 to Goette.are produced by evagination entirel)' frt)m the cdoJcnn of the lower end of the 

 throat-tube. 



Hyde, 1894 (Zeit. fiir wissen. Zool., Bd. 58, p. 521), finds, however, that in the case 

 of JuitUia only the upper floor of the second pair of stomach- pouches is formed from 

 the ectoderm o\' the throat-tube, their lower (aboral) floor being of entodermal origin and 

 derived from the wall of the priniiti\e stomach. Hvdc 's research appears to be ver\' care- 

 fully prepared, and it is probable that the second pair of stomach-pouches in Cot\'lorhiza is of 

 mixed (ectodermal and entodermal) origin as in AurAlia. The apparent analogy between the 

 ectodermal oesophagus of the young sc\phostoma and that of the Anthozoa is ver\' interesting, 

 lor it ma\' imply a close generic relationship between the Anthozon and the Scyphomedusic. 



In this connection we must, however, trive due wei"ht to the work of the Claus-Had/.i 

 school (see Genus Chr\saora) who find that the 4 primar\- stomach-pouches and the lining of 

 the throat are wholly of entodermal origin, and that therefore the scyphostoma resembles the 

 hydropohps more closeh' than the Anthozoa. 



The scyphostoma develops 16 tentacles and then gives rise to buds which grow out 

 from the sides of the body. The wider end of the pyriform bud is adjacent to the parent 

 scyphostoma, and the mouth is at this broad end. The bud is set free and swims, rotating 

 through the water with its narrow posterior end directed forward. Soon, however, the bud 

 attaches itself to the bottom by means of its narrow aboral end and then develops into a new 

 scyphostoma. 



This asexual development of lateral buds by the scyphostoma of Cotylorhiza seems to 

 be a normal process and is described by Goette, 1887, p. 24, and Claus, 1892. Claus, 1892, 

 reared Cotylorhiza in an aquarium and found that eggs laid at Trieste in September developed 

 into scyphostomae with 16 tentacles and then began to produce lateral buds in the following 

 July. 1 hey strobilated in August. The stroi)ilr/.ation is monodiscus, ihe scyphostoina giv- 

 ing rise to one eph3'ra. The 8 marginal sense-organs are apparently developed out of the 

 bases of the 8 perradial and interradial tentacles, while the 8 adradial tentacles degenerate 

 and are absorbed. A similar process takes place in Cnsslopea xamachatia, according to R. P. 

 Bigelow, 1900. The gelatinous substance is secreted by the entoderm. 



Claus, 1883, has studied the young ephyra; of Cotylorhlzii tubcrculata. When onl)- 1.75 

 mm. wide the ephyra has a simple 4-cornered mouth similar to that of the single-mouthed 

 Scyphomedusae. There are 8 long, slender, cleft lobes in the radii of the 8 marginal sense- 

 organs. The central stomach gives rise to 16 blindl\- ending radiating diverticula, 8 in the 

 radii ot the marginal sense-organs and 8 adradial in position. There is no ring-canal. These 

 canals are lined h\ unicellular \ellow-brown algx- {ZoochlorALc). There are 4 gastric cirri, one 

 in each interradius. The 4 lips are simple and cruciform and devoid of a marginal fringe of 

 tentacles. When about 2.25 mm. in diameter the oral fringe of tentacles begins to develop 

 around the edges of the still cruciform mouth. When 2.5 to 3 mm. wide the ring-canal develops 

 by fusions between the adjacent edges of the 16 radiating canals, and 8 adradial velar lappets 

 begin to grow out from the deep notches between the 8 primitive ephyia-lobes. 



When 3 mm. wide each quadrant of the cruciform mouth is bifurcated twice, giving 16 

 terminal forks to the entire mouth. The central mouth, however, still remains open. At this 



