NUCLEAR CONSTANCY IN IIYDATINA. 87 



mounts of Hydat'ma scuta prepared by Powers and Powers of 

 Lincoln, Nebraska. The excellence of the cytological details 

 displayed by these mounts speaks well for the methods employed 

 in their preparation. Nuclei of the vitellarium, stomach, gastric 





TEXT-FIGURE A. Photograph of a whole mount of Hydatina. The vitel- 

 larium is the large gland, with conspicuous nuclei, near the center of the 

 body. The gastric glands show as bean-shaped organs anterior to the vitel- 

 larium and attached to the sides of the stomach. 



glands, intestine, and some other structures are readily observ- 

 able and sharply differentiated from other structures. 



The ultimate source of the cultures from which these mounts 

 w T ere made has not been determined. According to Shull's ob- 

 servations (1918: 460) this does not seem to be of any great im- 

 portance for deviation in nuclear numbers seems to be inherent in 

 the various cultures examined by him. Age, culture media, and 



