28 CCELENTEEATA. 



10. Study the cellular structure of a hydranth and of a gon- 

 angium, as seen in cross and longitudinal sections. 



Make a drawing of each. 



For comparison use any thecate forms, which may be offered 

 as loose material or as demonstrations, such as Campanularia, 

 Sertularia, and Plumularia. 



PARYPHA. 



This form is frequently abundant on the piles of old wharfs, 

 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, hydrothecae, and gonangia. 



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 

 manubrium. 



3. The short but rather large body of the hydranth passes 

 back to the perisarc as the fleshy axis, coenosarc. 



4. Notice the medusa buds on the manubrium between the 

 rows of tentacles. What is their arrangement? This is a form 

 in which the medusae are not set free, but remain vestigial. 

 The gonads ripen on the partially developed manubrium of 

 the medusa. The sexes are separate. 



Make a drawing of a hydranth. 



5. The arrangement of the attached medusas is best seen in 

 sections. In the male medusae numerous spermatozoa will be 

 found, while the female individuals have a much smaller number 

 of large ova, which are likely to be in advanced stages of seg- 

 mentation. 



The sections show the same body layers as Hydra, and the 



