CAMPANULARIA. 29 



8. Examine a hydranth with a high power and look for the 

 cell-layers characteristic of ccelenterates. Determine how its 

 tentacles differ from the tentacles of Hydra, and explode nemato- 

 cysts as in Hydra. 



Make a drawing of a hydranth. 



9. Look for certain extremities which show neither tentacles 

 nor any opening in the outer covering. Such a condition sig- 

 nifies either an immature hydranth or a reproductive indi- 

 vidual. If the latter, it is considerably swollen and is termed 

 a gonosome. The central core of a gonosome, the hlastostyle, 

 should be examined for gonophores, frequently called medusce 

 buds. This may require a high power. Determine how the 

 gonophores are arranged around the blastostyle. Are all in 

 equal stages of development? What relation has the end of the 

 blastostyle to the outer covering, the gonangium f 



Make a drawing of a gonosome. 



10. The free medusae are small, transparent, and easily 

 overlooked. During the breeding season they may usually 

 be found in abundance in dishes in which colonies have been 

 kept over night. Notice their movements and their positions 

 while at rest on the bottom. The number of tentacles and the 

 position of the sense organs is definite for the species. Two 

 species that differ in the number of tentacles are common at 

 Woods Hole. The inverted bell with the manubrium sticking 

 out from the convex surface of the resting specimen is char- 

 acteristic for this form. Notice the quick reversal when the 

 animal swims. The radial canals are easily seen, but the gonads 

 are not developed at the time of liberation. The velum is very 

 small. 



Gonionemus is a more favorable medusa to study. This 

 form is valuable for comparison. 



CAMPANULARIA. 



In structure and habits this form is so much like ObeHa that 

 it is not easy to distinguish the two genera without studying the 

 gonosomes. Several species are found at Woods Hole, two of 

 which are usually abundant during the summer. 



