Cytomorphic structure was studied in erythrocytes ofBatrachoseps salamanders, a genus unique among non-mammalian vertebrates because most of the erythrocytes are anucleate. These anucleate erythrocytes are highly flattened, quite variable in size, and generally elliptical. All of them were found to contain marginal bands of microtubules (MBs), as observed in phase contrast and darkfield after Triton lysis. The MBs of larger cells typically twisted into figure-8 forms upon lysis. Whole mounts of the lysed anucleate cells consisted only of the MB plus a trans-MB network of material (TBM), as observed by electron microscopy. If lysis was carried out in the presence of 0.5 M KCl, all of the MBs circularized immediately and none were twisted. The network (TBM) was now missing, suggesting that it is needed for maintenance of MB ellipticity and plays a role in MB twisting. Small numbers of living anucleate erythrocytes were constricted in their mid-region, and others were pointed at one end. Correspondingly pointed MBs were observed after lysis, exhibiting a range of forms compatible with the mechanism proposed byEmmel (1924) in which the anucleate erythrocytes arise by amitotic division of nucleated ones.
The results show that these erythrocytes retain the typical nonmammalian cytomorphic system, and are thus unlike those of adult mammals. The network component (TBM) is present even though nuclei are absent, making it unlikely that it functions simply to position the nucleus. The observations are consistent with the hypothesis that the flattened, elliptical shape of non-mammalian vertebrate erythrocytes is generated by TBM tension applied across the faces of the MB “frame”, and that excessive tension induced by lysis (without KCl) produces MB twisting.