HYDROCORALLINA. SIPHONOPIiORA. AURELIA. 27 



Make a drawing from the side, slightly tipped, to show the velum, 

 and another as seen from the oral surface. 



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 characteristic 

 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 follow- 

 ing structures: (a) pneumatophore, (b) dactylozooids, (c) gastro- 

 zooids, (d) gonodendrons, (e) tentacles. It will be well to refer 

 to a text-book to find the positions and functions of each of 

 these. 



SCYPHOZOA. 



AURELIA. 



This form is one of the common jelly-fishes, and is found 

 floating freely in the water. It is frequently washed up on shore. 

 To be appreciated these medusae should be seen as they occur 

 at the surface of the sea, before they have been handled or in- 

 jured. Frequently vast numbers may be seen together, all 

 gently pulsating and thus keeping near the surface. The move- 

 ment is very different from that of most hydrozoan medusa, 

 being very deliberate and graceful. 



If living material is offered, study the method of locomotion 

 and compare it with the locomotion of Gonionemus. Like the 

 latter, the discoid animal presents ex-umhrellar (aboral) and suh- 

 umhrellar (oral) surfaces, but the edges of the disk are indented, 

 fringed with very numerous short tentacles, and a velum is 

 wanting. What difference does the velum make in locomotion? 



The ex-umbrellar surface presents little of interest. In the 



