232 V. A. DOGIEL 



since under bad life-conditions, continuing for a longer space 

 of time, the exconjugants of the first conjugation would hasten 

 to reconjugate, so as to become again more resistant to their 

 surrounding medium. 



EXPLANATION OF PLATE 17. 



All figures depict Ophryoscolex janus n. sp. and were 

 drawn with the help of Abbe's apparatus, under a Zeiss 2 mm. 

 homogeneous immersion objective with compensating ocular 

 no. 4. The figures were reduced to three-quarters in re- 

 production. 



Fig. 1. — A neuter individual. 



Fig. 2. — Conjugation between a macro- and microconjugant. Each 

 individual has a single macronucleus and two micronuclei. 



Fig. 3. — A micro-exconjugant with a synkaryon and the remains of the 

 old macronucleus. 



Fig. 4. — A macro-exconjugant with synkaryon ; the old macronucleus 

 is dissolved. 



Fig. 5. — A micro-exconjugant with old macronucleus (Oma), new 

 macronucleus (Ma), and rew micronucleus {3Ii). 



Fig. 6. — An ordinary fission of . janus giving rise to a pair of neuters ; 

 note the skeletal plate {Skp2) in the posterior individual. 



Fig. 7. — A progamic fission of O . janus; note the absence of a skeleton 

 from the posterior individual and the large size of the micronuclei {-Mi). 



Fig. 8. — A micro-preconjugant. 



Fig. 9. — A macro-preconjugant. 



Fig. 10. — Conjugation between two macroconjugants. 



Fig. 11. — An abnormal case of conjugation ; all the micronuclei {Mi^- 

 Mi^) lie in the macroconjugant, the microconjugant retaining only the 

 old macronucleus. 



Lettering. 



Adz, adoral zone of cilia. Cpr, conjugation process of endoplasm. 

 D, oblique diaphragm. Dz, dorsal crescent of membranellae. Ma, macro- 

 nucleus. Mi\ micronucleus. Oma, old macronucleus. Phm, pharynx. 

 a, rectum. Skp, skeletal plate. Si/, synkaryon. Fj, anterior vacuole. 

 V2, posterior vacuole. 



