86 Reproduction and Life-Cycles 



ciliates with a firm cuticle, fusion, or sometimes merely adhesion, may 

 involve a limited area of the body such as the left margin of the peristome 

 in Euplotes (234). 



As a rule, the micronucleus undergoes three pregamic divisions (Fig. 



Fig. 2. 19. Pairing in conjugation. A. Nyctotlienis cordiformis; x430 

 (after Wichterman). B. Pleurotricha lanceolata; x275 (after Manvvell). C. 

 Ancistroconm niyae, fusion of posterior ends; x2395 (after Kofoid and 

 Bush). D. Cycloposthium bipalmatuin, adoral organelles omitted; diagram- 

 matic (after Dogiel). E. Scyphidia ameirui; diagrammatic (after Thompson, 

 Kirkegaard and Jahn). F. Vorticella microstoma; x700 (after Finley). G. 

 Euplotes (patella) eurystomiis: x346 (after Turner). 



41, A-D). More commonly the second, but sometimes the first (101) of 

 these, is reductional. However, exceptions to the usual pattern have been 

 noted. The third pregamic division is sometimes omitted in Paramechim 

 trichium (72), and micronuclei may even be exchanged just after the first 

 division (73). When several or many micronuclei are present, the num- 



