During the examination of Brachionus plicatilis (Rotifera, Monogononta), ectosymbiotic bacteria were found in the ciliated buccal region. These have about the same dimensions as the cilia and possess a specific apical region that apparently serves to attach the bacterium to its host cell. This apical region resembles a vesicle but is interpreted as a specialized region of the bacterial nucleocytoplasm devoid of ribosomes and chromatin strands but containing a crystalline rod. The bacterium has two membranes (as have other Gram-negative bacteria) also over the apical region. Thin strands join the two membranes and similar strands extend from the bacterium to the cell membrane of the host cell. No intracellular bacteria were found in this study.

AbstractIn a man with a pituitary prolactin‐secreting adenoma almost only double spermatozoa were produced. These cells were almost completely enveloped in a unique membrane, a common bilocular acrosome capped two paired nuclei, and all the other organelles were double. After 120 days of treatment with 2‐brom‐α‐ergocryptine the prolactin level was corrected, and only normal, single spermatozoa were produced. The authors suggest that a high prolactin level inhibits cell division.

The spermatozoon of the Onychophoran Peripatopsis moseleyi is described. This cell is characterized by the general filiform shape, the absence of an acrosome, the presence of mitochondrial derivatives, of an annulus and of nine accessory tubules and a manchette of microtubules around the axoneme. All of these characters are typical of highly evolved sperm models, like those of insects and mammals, and suggest a long evolutionary history. Only the position of the mitochondria, inserted between nucelus and axoneme, is reminiscent of annelid features.

The spermatozoon of Bacillus rossius is peculiar in many respects. The acrosome bears only the two outer layers, and the Golgi complex is involved in the building up of a large number of flagellar structures. In fact, it has been observed that a group of Golgi-derived cisternae analogous to the proacrosomal ones become arranged around the original 9+9+2 axoneme forming the two laminated accessory bodies and also supplying the nine outer tubules with carbohydrates. Other cisternae that migrated peripherally partially replace some plasma membrane areas. Furthermore, the Bacillus sperm represents a unique model by virtue of other characteristics more directly involved in the problematics of metabolism and motility, which are closely interdependent. These characteristics are as follows:1.Absence of mitochondria and presence of anaerobic glycolysis alone.2.Different categories of organelles endowed with ATPase activity cytochemically identified. These organelles are the postcentriolar region, the doublet arms, the central sheath, coarse fibers (corresponding to the zones intervening between accessory tubules), accessory laminated bodies (characteristic of the spermatozoon in Phasmoidea alone, located in the position occupied as a rule by the mitochondrial derivatives). Demonstration of ATPase activity and the morphological changes of all these structures that are protein in nature, during the different torsion states of the spermatozoon suggest that they may be endowed in some way with contractile activity.3.The anterior region of axoneme as origin of the motion.4.Propagation of two superimposed wave systems of different amplitude and frequencies. This phenomenon is explained as the occurrence of two different flagellar components, each responsible for the propagation of a wave system. The different frequencies are imagined to be a consequence of the ATPase catalytic characteristics; the amplitudes derive from the mechanical properties of the propagation structures. The evidence presented above suggests that the axoneme and the laminated bodies are responsible, respectively, for the propagation of the high-frequency and the low-frequency waves.