662 MKDUS.E OF THE^WORLD. 



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

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

 as in the case of Aurellia. The free-swimming planula is pyriiorm 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 by 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 Goette 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 mouth and oesophagus; while the entodermal evaginations form the first pair of 

 lateral stomach-pouches. An opening is soon iormed where the invagmated 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 entirely from the ectoderm ot the lower end of the 

 throat-tube. 



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

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

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

 derived from the wall of the primitive stomach. Hyde 's research appears to be very care- 

 fully prepared, and it is probable that the second pair of stomach-pouches in Cotylorhiza is of 

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

 ectodermal oesophagus of the young scyphostoma and that of the Anthozoa is very interesting, 

 for it may imply a close generic relationship between the Anthozoa and the Scyphomedusae. 



In this connection we must, however, give due weight to the work ot the Claus-Had/.t 

 school (see Genus Chrysaora) who find that the 4 primary stomach-pouches and the lining ot 

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

 hydropolyps more closely than the Anthozoa. 



The scyphostoma develops 1 6 tentacles and then gives rise to buds which grow out 

 from the sides of the body. The wider end of the pyritorm 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 Cotylorluza 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. They strobilated in August. The strobilization is monodiscus, the scyphostoma giv- 

 ing rise to one ephyra. 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 Cassiopea xamachana, according to R. P. 

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



Claus, 1883, has studied the young ephyrae of Cot\lor/uza tuberculata. When only 1.75 

 mm. wide the ephyra has a simple 4-cornered mouth similar to that ot 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 blindly ending radiating diverticula, 8 in the 

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

 canals are lined by unicellular yellow-brown algae (ZoochlorelLr). 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 ephyra-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 



