56 KANSAS UNIVERSITY SCIENCE BULLETIN. 



tidce along with that of other animals. He saw the object formerly described by 

 St. George and named it "nebenkern." He saw it divide into halves, elongate, 

 and form the spermatozoon tail. 



The dividing of the nebenkern into halves seems to be an ap- 

 pearance quite common in insect spermatogenesis. I have my- 

 self seen it in several genera of Acrididse — Hippiscus, Arphia, 

 Melanoplus, and Brachystola ; besides Bntschli, St. George,. 

 Henneguy, Platner, Paulmier and others have described it. 



Platner in his studies has given special attention to the nebenkern. In his 

 first paper on "Pulmonates" ('85) he did not trace the origin of the nebenkern, but 

 described it as consisting of four to six rods of different lengths and irregularly 

 bent. These were connected, forming an irregular polygon. In its later stages 

 he saw it with a mass of protoplasm pass down along the primary tail — an early 

 protrusion of protoplasm. Finally it is lost. 



In his succeeding paper ('86, 1) he studied the "nebenkern" spindle remains 

 — in the spermatogonia and spermatocytes of pulmonates. In the spermatids,, 

 as in the former generations of cells, the nebenkern grows out of the nucleus,, 

 where it, with the chromatin, had formed the spireme. It appears as a loop,, 

 which becomes larger, twisted, and entangled, and finally breaks loose from the 

 nucleus. Later it goes to form the spiral covering of the primary tail, changing 

 it to the axial filament and true tail. 



In his next paper ('86, 2) he describes the changes when the dividing of the 

 protoplasm lags behind in the spermatocyte divisionsf His description agrees in 

 so many points with my own, that I shall quote his exact words: 



"Die Spindelfasern hingegen contrahiren sich mehr und mehr nach dem 

 Equator hin, wobei sie mit ein ander verschmelzen und merkwiirdiger Weise 

 je weiter dieser Verdichtungsprocess fort schreitet um so mehr an Tinctions 

 fahigkeit speciell gegeniiber dem Hamatoxylin gewinnen. Sie stellen jetzt 

 zwei dreieckige oder hakenformige Gebilde dar, die mit der Spitze noch im 

 Equator zusammenhangen mit der breiten Seitesind sie den zugehorigen Zellen 

 zugewendet. Hier sind ihre Grenzen undeutlicher, verwaschen und zeigen hier 

 auch noch hauh'g eine streifige Beschaffenheit, welche auf ihren Ursprung hin 

 weist. Zuweilen lassen sich einzelne Faden noch eine betrachtliche Strecke weit 

 in das Protoplasma hinein verfolgen, welches zwischen ihnen und den sich aus- 

 bildenden Zellkernen liegt." 



The "hakenformige Gebilde " moves away from the periphery, its sides elon- 

 gate, break, and unite at the nuclear end, thus form the polygonal nebenkern. 

 "Derselbe geht also in diesem Falle direckt aus den Spindelfasern hervor." 

 When the protoplasm does divide a similar process takes place. The spindle 

 remains divide at an equatorial line and each half forms a nebenkern, and, as he 

 says: "Also auch hier geht der Nebenkern direckt aus den Spindelfasern 

 hervor. Vielleicht geht in den Spermatiden der Nebenkern uberhaupt immer 

 aus den Spindelfasern hervor, in dem die langfiidige Verbindiingsbriicke, die ihn 

 oft mit dem Kern verbindet, sich wohl als ein noch einige zeit persisttirender 

 Rest der esteren deuten lasst." 



In his paper on Limax ('89, 1) he followed the nebenkern through all the di- 

 visions and thinks it a constant organ of the cell. In the second part of the pa- 

 per on Helix and Paludina the nebenkern was considered as formed from the 

 remains of the spindlepole and the centrosome. Later Platner ('89,2) found the 

 nebenkern in the pancreas cells. In reports upon Pygazrq and Sphinx he 



