Heteronemertea 163 



For a study of asexual reproduction or regeneration each worm or tiny 

 fragment may be kept in a separate, cork-stoppered, 6- or 8-dram vial 

 containing clean seawater only, changing the water every day or every 

 few days. 



The smaller representatives of each of the orders, except the parasitic 

 Bdellonemertea, may be kept in the same manner but somewhat less 

 successfully. The larger forms naturally require vessels with a generous 

 supply of water and a thicker layer of bottom material. 



FRESHWATER SPECIES 



Species of Prostoma (Stichostemma) are found adhering to the leaves 

 of aquatic plants in pools and quiet streams in nearly all parts of the 

 United States. They thrive in aquaria containing a good growth of 

 vegetation if supplied with minute Crustacea, nematodes, turbellarians, 

 and other small organisms, but the water must be free from bacterial 

 decomposition. The plants will require a thin layer of soil on the bottom 

 of the aquarium. Excessive evaporation is prevented in arid rooms by 

 partially covering the aquarium with a pane of glass. Prostoma thrives 

 best at temperatures of about 20 C. Egg clusters are deposited along 

 the sides of the aquarium at all seasons of the year. 



TERRESTRIAL SPECIES 



Greenhouses having soil, temperature, and moisture conditions suit- 

 able for the cultivation of ferns and moisture-loving tropical plants are 

 suitable for the culture of Geonemertes. The worms are merely allowed 

 to burrow in the moist soil of the pots or boxes containing the plants. 

 They are protandric, with sexual reproduction only. Egg masses are 

 deposited on or near the surface of the soil. 



OBTAINING EGGS FOR EXPERIMENTAL PURPOSES 



As stated in the preceding sections, the smaller species, such as Lineus 

 and Prostoma, deposit their eggs in gelatinous clusters when the nemer- 

 teans are cultured in the laboratory, and in both these genera the eggs 

 develop readily in the jars or aquaria without special precautions. For 

 studies on maturation and fertilization and especially for experimental 

 work where very large numbers of ova are necessary, the larger littoral 

 forms, such as Cerebratulus or Micrura, are easily secured in the breeding 

 season. 



A very large female Cerebratulus lacteus which occurs in the intertidal 

 zone along the entire Atlantic coast of the United States may produce at 

 one time upwards of fifty million eggs. These are mature in early spring 

 along the Carolina coasts, during May and June in Long Island Sound, 

 in July at Woods Hole, and during July and August in Massachusetts 



