It has long been known that ticks possess spermatozoa that differ considerably from the typical flagellate form. In similar cases science has always attempted to trace the aberrant type back to the normal with a view to identifying its constituent parts. Many forms, even those which at first sight appear incapable of being compared with the normal, have recently been thoroughly analysed in this manner. On the other hand there occur several types of spermium whose parts it is impossible to compare with those of the normal type and in these instances all that can be done is to identify the elements that take part in the fertilization, viz. the nucleus and centrosome.