54 COELENTERATA 



3. Break a shell and place the fragments incrusted side up 

 in a watch glass of sea water and examine with a low power. 

 Three kinds of individuals will be apparent: (a) large indi- 

 viduals with long tentacles. These are the feeding hydranths. 

 They differ somewhat in appearance in the male and female 

 colony. The male individual has a large proboscis, while the 

 female individual has only a slightly arched disk with the 

 mouth in the center, (b) Reproductive individuals with 

 knoblike tentacles, a proboscis that is usually retracted, a 

 mouth, and with gonophores along their sides. In female 

 gonophores the manubrium and a number of eggs may be 

 seen. These gonophores never become detached and never 

 show further medusoid structure, (c) Elongated individuals, 

 especially near the outskirts of the colony, that have rounded 

 tentacles, proboscis, and mouth like those of the reproductive 

 individuals. These sometimes branch and have a habit of 

 bending the head toward the base or even twisting the body 

 into a spiral. They are not distinguishable from the repro- 

 ductive individual except by shape and the fact that they 

 have no gonophores. 



4. Notice that the individuals are connected at the bases 

 by a fleshy layer which is responsible for the deposit already 

 mentioned. 



Make a drawing of each kind of individual. 



HYDROCORALLINA 



To this group belong forms that have heavy calcareous 

 exoskeletons. While material is generally not at hand to 

 study the polyps, it is desirable to study and sketch the char- 

 acteristic forms of colonies such as Millepora and Stylaster, 

 and to note the difference in the distribution of pores. Later 

 you will see how decidedly these differ from the ordinary 

 stony corals. 



SIPHONOPHORA 



Examine living or preserved specimens of Physalia, and 

 sketch the type with reference to showing, if possible, the 



