Memoirs: The Neuromotor System of Euplotes patella during Binary Fission and Conjugation

Abstract

1. The neuromotor system of Euplotes patella Ehrenberg was studied in different stages of the life-cycle, including the adult, and asexual and sexual reproduction. 2. In the adult the basal granules of all the cirri are arranged in straight primary and secondary rows. The fibrils from the bases of the cirri are in general parallel with either the primary or secondary rows of basal granules of the cirri to which they are attached. This is interpreted as an indication of the evolution of the organism from an ancestor with a simple neuromotor system in which the cilia were uniformly distributed over the surface of the body in longitudinal, slightly spiral rows. 3. The basal apparatus of a bristle consists of a basal granule at the bottom of a depression in the ectoplasm which is surrounded by a group of rodlets and ends at the surface in a ring connected with the polygonal system. The polygonal or silverline system is pellicular in position. 4. During asexual reproduction the entire set of cirri is resorbed and replaced by two new sets of cirri, one for each daughter. One frontal cirrus for the anterior daughter develops in the old peristomial field of the parent, while the corresponding cirrus for the posterior daughter develops in the new peristome. The right marginal cirri arise on the dorsal surface along the rows of bristles and later move to the ventral surface. The fibrils develop outward from the bases of the cirri. 5. During binary fission a new peristome arises in a depression in the ectoplasm independently of the old peristome. The old peristome remains in the anterior daughter without at the time undergoing any visible change in structure. 6. The multiplication of the bristles is limited to a zone on either side of the future plane of constriction. Multiplication occurs by a series of fissions of the basal granules in this area. Dedifferentiation of bristles was not seen. 7. The polygonal system is replaced over the entire surface of the body with the exception of the old peristomial field. The new system originates in many separate loci in connexion with the bristles on the dorsal surface, and with the rudiments (Anlagen) of the cirri and peristome on the ventral surface. 8. During conjugation there are two successive reorganizations of the neuromotor system, that of the ‘gamete’ (conjugant) and that of the zygote. 9. The first reorganization, that of the gamete, begins during the maturation divisions preparatory to fertilization. During this reorganization the posterior portion of the peristome is resorbed and the remaining anterior portion is later replaced. The eighteen cirri are replaced by a set containing only seventeen cirri. 10. The second reorganization, that of the zygote, occurs during the differentiation of the nuclei in the exconjugants. It involves the completion of the peristome by differentiation of the missing posterior portion, and the replacement of the set of seventeen cirri by a complete set of eighteen cirri. 11. These protoplasmic reorganizations, invariably associated with both asexual and sexual reproduction, involve a structural and presumably a physiological rejuvenation resulting in the possibility of an indefinitely continued existence of the individual in the Protozoa. It may be that sexual reproduction is not necessary to bring about this result, but further work on the relationship of endomixis to the problem is needed.