3 2 



A ROTIFER. 



STRUCTURE. Identify and examine the following parts: 



a) The broad anterior region called the trunk, terminating posteriorly 



in a slender, two-forked tail. 



b) In some genera the trunk is enclosed in a transparent outer sheath 



of cuticle, the lorica. Does the specimen you are studying have 

 such a glassy shield? 



c) The anterior end of the trunk forms the trochal disc, with its 



cilia usually arranged in one or two circular rows. It is the vibra- 

 tory movement of these cilia that presents the appearance of a 

 rotating wheel, thus giving the animal its name. Determine 

 whether or not the trochal disc is in any degree retractile. 



d) Are there any elevations ciliary lobes on the trochal disc? 



If so, how many and where located ? How do the cilia on these 

 compare with those on the other parts of the disc? 



e) By introducing a little coloring matter under the slide and watching 



the currents about the circlets of cilia one may locate the mouth 

 in the ventral region of the trochal disc. The anus is dorsally 

 placed at the junction of trunk and tail. 



f) Look for eggs attached to the animal exteriorly near the base of the 



tail. 



g) Rotifers are usually transparent enough that some details of the 



interior structure may readily be made out. Conspicuous, near 

 the front of the trunk, is the mastax, a complicated grinding appa- 

 ratus for reducing the food to fine particles. Watch carefully its 

 movements and describe the process of grinding in your notes. 



h) Anteriorly the mastax is connected with the mouth by a short 

 gullet, and posteriorly it is followed by an enlargement, the 

 stomach, and a short intestine ending hi the anus. Make out 

 as much of this digestive tract as possible. 



i) A convoluted tube may be more or less discernible along either side 

 of the trunk. These tubes are the nephridia, the main organs of 

 excretion. 



j) Look for a single nerve ganglion, the brain, just ahead of the mas- 

 tax. On the top of this ganglion is a small red eye-spot. 



k) When the animal stretches itself out you may be able to see some 



