100 ERNEST WARRKN. 



(h. G.). the siipei-iniposed attenuated perisarc {d. p.), and the youngest 

 observed ovum (0.) embedded in the endoderm. 



Fig. 2. — x 220. Lono-itndinal section tlirough a young gonangium 

 showing the ovum (0.) being thrust out into a special thickening of tlie 

 ectoderm, whieli early becomes differentiated into an outer io. 1.) and an 

 inner layer (/. /.) and represents the ectodermal portion of a reduced 

 gonophore. The slight space between the two layers is equivalent to 

 the uml)rella-cavity of a medusa. 



Fig. 3. — X 260. Transverse section through a young gonangium, 

 showing the ovum surrounded by the ectoderm of the gonophore. sp. is 

 the space which arises between the outer ectodei'm of the gonophoi'e and 

 the ectoderm of the reduced umbrella-cavity. 



Fig. 4:. — x 220. Longitudinal section through a slightly older 

 gonangium. The gonophore, consisting entirely of ectoderm, is more 

 developed. The outer layer (o. I.) is now well-defined, while the inner 

 layer {i. I.) closely surrounds the ovum (0.). The ectoderm of the gonan- 

 gium at the distal surface has thickened considerably and forms the 

 "covering cap" {c.f).). The space {sp.) is clearly seen. Spaces (sp.,,sp..,) 

 are appearing l^etween the pei-isarc of the gonotheca and the general 

 ectoderm. The endoderm immediately under the gonophore ectoderm 

 is inoi"e granular than the remainder of that layer. 



Fig. 5. — X 220. Longitudinal section through an older gonangium. 

 The outer layer of ectoderm (o. Z.) has become more fiattened through 

 pressure exerted l)y the expanding inner layer (/. /.). Beneath the gono- 

 phore the endoderm is beginning to grow and to form a diverticulum 

 of the ccelenteron which i-epresents the ccelenterou cavity of the reduced 

 gonophore. 



Fig. 6. — x 220. In this older stage the longitudinal section shows a 

 well-defined space (c. 0.) between the ovum and the ectoderm {i. 1.) of the 

 gonophore. The ovum is svirrounded by a membrane which is more 

 marked externally than on the inner surface, which is in contact with 

 the endoderm. 



Fig. 7. — X 220. Longitudinal section of gonangium at right angles 

 to the plane of flattening. Here the cavity (c. 0.) of the gonophore has 

 expanded, and the meml)rane around tlie ovum (r. vi.) is thickened. 



Fig. 8. — X 220. Longitudinal section of gonangium in the plane of 

 flattening. This is in the same stage of growth as in fig. 7. 



Fig. 9. — X 220. Longitudinal section at a, later stage. The ectoderm 

 layer of the gonophore has broken down (e. G.), and forms an irregular 

 mass of tissue around the ovum. The endoderm below is granular and 

 in an active condition of growth. The cells of the distally placed 



