TUBULARIA. 33 



seen along the edge of the bell). They are filled with a layer 

 of strongly pigmented endoderm cells and are probably light- 

 percipient organs. 



(b) Other small sessile and transparent outgrowths, situated 

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

 which are probably static organs. 



All of the tentacles are abundantly supplied with tactile, 

 sensory cells. There is a well-established circum velar 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 Hydromedusse. 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. 



: Gonionemus, Science, 1926, p. 93. 



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

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



TUBULARIA. (Parypha.) 



This form is frequently abundant on the piles of old wharfs 

 and on rocks, where the colored colonies form conspicuous masses 

 just below low-water mark. 



Examine the general form of a colony and note, either with 

 a hand lens or with the naked eye, the stem, or hydrocaulus, as 

 it arises from the branching, matted hydrorhizal portion of the 

 colony. The parts of the colony will be seen to differ from the 

 Leptomedusan (Campanularian) form studied, especially in 

 branching, rigidity, hydrothecse, and gonosomes. 



Make a drawing to show the formation of the colony. 



1. How does a hydranth differ from the hydranth of Obelia 

 in the matter of tentacles? Is a hydrotheca present? 



2. The mouth is terminal and is situated at the end of a 

 proboscis, 



3 



