458 BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



1907 and Metcalf 1909). Abnormal Cepedea dimidiata with slen- 

 der appendages appear in starved cultures (see Neresheimer 

 (1909) and von Linden (1909)). Valuable detailed observations 

 are recorded as to the structure of pellicle, (Euciliate-like) 

 ectoplasm and entoplasm. Formation of chromidia from the nuclei 

 is described as occurring throughout life (confirming Metcalf (1909) ). 

 At no time do these give rise to nuclei, the generative nuclei being 

 derived from the sexual nuclei by mitosis (confirming Metcalf 

 (1909) against Neresheimer (1907)). The endosarc spherules are 

 regarded as macronuclei because (1) they divide amitotically (con- 

 firming Tonniges (1898) against Metcalf (1909) ) ; (2) they dis- 

 appear before the completion of conjugation. [This is not the case 

 in Protooyalina intestinalis or in P. caudata and apparently, from 

 my preparations, is not true of Cepedea demidiata or Opcdina rana- 

 rum. The endosarc spherules seem to decrease in number and may 

 even disappear wholly from the infection cysts. They become again 

 evident in the young Opalinids hatched from these cysts in the recta 

 of the tadpoles. Both macrogamites and microgamites have endosare 

 spherules in numbers proportional to the size of these animals and 

 the same thing is true of the zygotes. Among the Euciliata the 

 macronucleus is always a true nucleus having been derived origi- 

 nally from an ordinary nucleus by mitosis. The formation of nuclei 

 from chromidia in any Protozoa is extremely improbable, the " best 

 authenticated" instances of this process having been shown by 

 Kofoid (1921) to be unfounded. Until the origin of endosarc 

 spherules from normal nuclei by mitosis has been shown, the sug- 

 gestion that they are macronuclei can not be entertained.] 



Nutrition is by endosmosis aided by extra-cellular digestion; 

 experimental evidence of this is offered and the digestive vacuoles 

 opening by tubules through the pellice are described. Excretory 

 crystals are often abundant in the endoplasm. They increase espe- 

 cially during the period of encystment. Opalina Tanarum has a 

 well-developed system of excretory vacuoles opening posteriorly by 

 numerous pores, the middle one of which is the largest. 0. ranarum 

 and G. dimidiata are positively geotactic, and are indifferent to light 

 and currents. They gather at the anterior end of the rectum be- 

 cause this is lowest. Place a frog on its back for a time and the 

 Opalinids will be found abundantly in the posterior portion of the 

 rectum. [? (1) In most Anura the anterior end of the rectum is 

 the higher when the animal is sitting up ; it is always so in the char- 

 acteristic position at the surface of the water, and is hardly, if at 

 all, lower than the body of the rectum when the animal is crouching; 

 (2) the Opalinids are most numerous in the rudimentary caecum, 

 which is the dorsal region of the anterior end of the rectum; (3) 



