THE HYDROMEDUSAE 



A process of budding, similar in character but not followed by 

 a separation of progeny from parent, results in the production of 

 colonial forms (Figs. 16 to 20); in the colony thus formed, the 



Fio. 6. 



Fio. 7. 



5. Section of a medusoid, placed mouth upwards for comparison with a hydroid (Fig. 4). 

 The right half of the section is taken along a radial canal, the left half between two radial 

 canals. CC, circular canal ; EU, exumbral surface ; 0, gonad or generative cells lying in the 

 ectoderm of a process of the subumbral body wall (characteristic of Leptomedusae) ; (?, 

 gonad lying in the ectoderm of the manubrium (characteristic of Anthomedusae) ; GL, gastral 

 lamella ; A/, manubrium ; NR, the outer, and NK , the inner parts of the nerve ring ; RC, radial 

 canal ; SU, subumbral cavity ; T, tentacle ; V, velum. Body layers represented as in 



6. Section of a medusoid, at right angles to Fig. 5. Letters as in Fig. 5 ; body layers as in 

 Fig. 4. 



7. Diagram showing the chief radii of a medusoid. P, perradii (the first four radii 

 accentuated in development); /, interradii ; A, adradii. 



coelenteron of each hydroid communicates with those of all the 

 other hydroids through the tubular coenosarc or common tissues. 



