THE INVERTEBRATE COURSE. 1 05 



of Tubularia and Obclia. These are normally fruiting at the time 

 studied. A morning in which the student sees fruiting Tubularia 

 and watches Actinulce emerge and crawl around, added to an 

 afternoon studying Obelia which are shedding Encope, makes a 

 day's work that the instructors, at least, never forget. To insure 

 a plentiful supply of Eucopc or Actinnhc, the material is brought 

 into the laboratory a few hours before being studied and allowed 

 to stand in a shallow dish in fresh sea water. The Eucope come 

 out more readily if placed in the sun and are to be found on the 

 sunny side of the dish. 



Fruiting Endcndnnm-, Clava, Hydractinia, Schizotricha and 

 Sertularia are also available for observation and study. In 1921 

 following a mild winter and an early spring, we could obtain 

 fruiting Bougainvillia, Cainpanularia and Pennaria. Gonionemus 

 is studied alive in some detail and living Physaft.a is usually on 

 hand at some time in the six weeks. 



In Hydractinia the striking dactylozooids are readily demon- 

 strated by removing the hermit crab on who<se foster shell they 

 grow and stimulating one edge of the colony by scratching with a 

 needle. Under a low-power lens the wave of stimulus can be 

 followed across the colony as the dactylozooids strike. These 

 "persons " of the colony are more abundant near the mouth of the 

 shell than elsewhere. In Gonionemus, the lithocysts are readily 

 studied by cutting a V-shaped piece from the margin and mount- 

 ing aboral side up under the high power. 



The work on the development of Aurelia is on preserved and 

 stained material, although there are usually living Aurelia 'in the 

 laboratory, and sometimes enough of it to supply the class. The 

 canal system is here best demonstrated by injecting it with air, 

 which is easily done even in preserved specimens. 



With Metridium a half day is spent in repeating Parker's 1 ex- 

 periments on feeding reactions and an opportunity is given for 

 dissecting recently preserved specmens that have not yet lost all 

 their color. Prepared sections showing relations of the mesen- 

 teries are present for special study and living and preserved As- 

 ti-angia is at hand for those who have done the other work. The 



i " The Reactions of Metridium to Food and Other Substances," Bull. Mus. 

 Conip. Zool. Harvard, 29, 1896. 



