Observations on Various Sporozoa
Authors: Clarke J. Jackson 
Published: April 2021

Certain problems propounded in the last few years demand for their solution a closer study of the intimate structure of the sporozoa than has hitherto been found necessary. The variations of nuclear form presented by these organisms call for especially close examination. For some of the higher members of the group this work has been well begun by Wolters,1 who examined Clepsidrina blattarum, Monocystis magna and agilis in Lumbricus agricola, and Klossia in the kidney of snails. The description of the nuclear changes in the common gregarines of the earthworm is particularly complete, and since I have been able to confirm many of Wolters’s observations it may be of interest if they are briefly reviewed here. He found in Lumbricus agricola both Monocystis magna and agilis constantly present, and almost to the exclusion of other species. In both, at every stage, a distinct nucleus was present. In the former it was relatively large and oval, in the latter of a rounded form. Under compression the nuclear membrane ruptured, but the contents did not escape, and when the compression was removed the nucleus tended to return to its primitive form. Thus the nucleoplasm appeared to be of a solid structure. In M. agilis this was also observed. The nuclear membrane was found to be strong and sharply defined, and in the young parasite there was a single large nucleolus. Later the outline of the nucleus had become irregular and the nucleoli more numerous. In M. agilis, and in one instance in M. magna, Wolters encountered what he has named the flame-nucleus, a condition in which the nuclear membrane has disappeared, and the nuclear substance is prolonged at various points into the protoplasm of the body of the protozoon. As soon as the nucleolus has broken up into subdivisions the parasites are ripe for conjugation. It was found that after the syzygium was formed the nucleus of each parasite moved to the periphery, became elongated, and soon exhibited a typical nuclear spindle with the chromatin now massed together at the middle of the spindle. The chromosomes were very small. The division of each nucleus took place, and half of each nucleus was extruded as a polar body. Meanwhile the surfaces by which the parasites adhered to each other became altered in such a way that instead of the sharply marked line of division previously seen throughout a complete series of sections of a syzygium, there was at one part of the applied surfaces a communication through which the two parasites fused together. In each parasite the polar body was extruded on the surface opposite this communication, towards which, after the polar bodies had been formed, the two nuclei moved, and having reached the spot at the same time they fused together. After this a nuclear spindle was to be seen in each half of the syzygium, and could be distinguished, by its position close to the area of communication, from the spindles which were concerned with the formation of the polar bodies. Thus it appeared that the conjoined nuclei had undergone division, and that the daughter nuclei were again subdividing. The resulting two nuclei moved towards the periphery in each half of the syzygium, and there formed two spindles. This Wolters found to be the case in complete series of sections. These spindles were smaller than those of the polar bodies. By repeated subdivision these peripheral spindles and resulting nuclei increased in numbers and became surrounded by protoplasm constituting the sporogonia, which arranged themselves peripherally, and also in spaces extending from the periphery into the remains of the body substance of the parasite.