HYDROCOKALLINA. SIPHONOPHOBA. 31 



(6) Other small sessile and transparent outgrowths, situated 

 between the bases of the tentacles, are the so-called otocysts, 

 which are probably static organs. 



All of the tentacles are abundantly supplied with tactile, 

 sensory cells. There is a well-established circumvelar nerve 

 ring (not easily determined in living material) derived from the 

 ectoderm, also scattering nerve cells beneath the ectoderm in 

 connection with the muscular tissue. Ex-umbrellar and sub- 

 umbrellar layers of muscle fibers are also present. 



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

 and another as seen from the oral surface. 



Brooks: Life History of Hydromedusae. Mem. Bost. Soc. Nat. Hist., 3, 

 1886. 



Murbach: The Static Function in Gonionemus. Am. Jour. Physiol., 10, 

 1903. 



Perkins: The Development of Gonionema murbachii. Proc. Acad. Nat. 

 Sci., Phila., 1902. 



Yerkes: A Study of the Reaction Time of the Medusa Gonionema murba- 

 chii to Photic Stimuli. Am. Jour. Physiol., 9, 1903. 



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. 



Bigelow: The Siphonophorse. Mem. Mus. Comp. Zool., Harvard, 38, 1911. 



