PROTOZOA AS CELLS 59 



and 19, PL V). These are open at their inner ends, and are roughly 

 hexagonal in cross section, with a diameter of about 140 m/z; 

 their walls appear dense in electron micrographs and may be 

 double membranes. Where the tubes terminate at the nuclear 

 membrane, each is concentric around a pore. Lehmann (1958b) 

 noted the attachment of peripheral nucleoli to the inner ends of 

 the tubes by strands of delicate vesicles. Similar material appeared 

 within the tubes and outside the nucleus, and he speculated on 

 the possible passage of vesicular material from nucleoli to cyto- 

 plasm in this manner. Mercer (1959) also observed vesicular 

 material near the nuclear surface and postulated that it might 

 originate from the nuclear membrane. However, such vesicular 

 material is so similar to the wispy substance representing compo- 

 nents of the cytoplasmic matrix after fixation that it would at best 

 be difficult to demonstrate such a migration. 



The nucleus of Amoeba pro feus is large, up to 50 fj, in diameter, 

 and maintains its biconcave disc shape while floating in the 

 streaming endoplasm. Consequently it has been suggested that 

 the honeycomb layer of the nuclear cortex may have a function in 

 the maintenance of form. It is extremely interesting to note, then, 

 that more or less similar honeycomb layers have more recently 

 been found in three other protozoan nuclei. 



Beams, Tahmisian, Devine, and Anderson (1957) first reported 

 on the nuclear envelope of Gregarina rigida, & sporozoan parasitic 

 in the intestine of a grasshopper, and subsequently Grasse and 

 Theodorides (1957, 1959) published observations on a gregarine 

 from a tenebrionid beetle. The honeycomb layer, only about 

 90 m/x deep in these organisms, has the appearance of a dense 

 meshwork of filaments closely applied against the usual double 

 nuclear envelope but regularly interrupted by bulbous or conical 

 channels open to the nucleoplasm. Peripherally, the channels 

 again appear to be concentric to pores in the outer envelope. The 

 French authors, however, consider that the pore-like structures 

 are vesicles in a continuous membrane. 



In 1959, Beams and his colleagues found that Endamoeba blattae, 

 (distantly related to Amoeba), occurring as a parasite in the hindgut 

 of a cockroach, has an Amoeba-like honeycomb layer at the nuclear 

 surface, but that in this case it occurs on the cytoplasmic side of the 



