iv COELENTERATA 61 



which constitutes one of the creeping stolons. The narrow end 

 grows up and develops into the first polyp, the mouth and tentacles 

 being formed as described in Tubularia. Metschnikoff's results 

 have been confirmed in the most gratifying manner by Rittenhouse 

 (1910), who studied the development of the eggs of the medusa 

 Stomotoca apicata. The sole point in which he is inclined to differ 

 from Metschnikoff is, that he regards the endoderm as arising- by the 

 budding of cells from the cells constituting the blastula wall, rather 

 than from the migration of cells forming part of that wall into the 

 interior. Thus we see that processes, which in the case of Tubularia 

 are completed before the larva leaves the bell of the mother, do 

 not occur in the case of the free medusae till long after the larva 

 is fixed. 



FIG. 39. A young colony of Clytia reared from a plauula in the aquarium. 

 (After Metschnikoff. ) 



bl, blastostyle ; g, rudiment of medusa ; per, perisarc. 



A thorough study of the development of the medusae and gono- 

 phores has been made by Gotte (1907). In the series of progressive 

 modifications of development which can be constructed from the 

 development of the forms which he describes, Tubularia and 

 Pennaria (in which the medusae occasionally become free) take the 

 second place. The most primitive type of development is found in 

 forms like Podocoryne, in which the medusa regularly becomes a 

 free-swimming organism, and swims about for a long time, and eats 

 and grows before it develops genital cells. 



In Podocoryne, after the medusa-bud has attained the stage just 

 described for Tubularia, after the radial canals have been formed, 

 they give rise to lateral outgrowths which meet those of adjacent 

 radial canals, and in this way a circular canal is formed ; then the 

 freely-projecting ends of the radial canals give rise to free tentacles. 

 By the formation of flat solid extensions from the lateral walls of 

 the radial canals, which meet each other, a continuous sheet of 

 endoderm is formed which spreads over the whole extent of the bell. 

 This is called the endoderm lamella. The manubrium attains a 



