MATURAT[ON OF OVUM IN ECHINUS ESOULLINTUS. 211 



uuited to form rings. The chromatin material was then con- 

 densed on to four parts of the rings, which broke up to form 

 typical tetrads. These were distributed as dyads in the first 

 polar, and monads in the second polar spindle. Vom Rath 

 held that each of these bodies represented a single chromo- 

 some, and that both divisions were '' reducing." There is thus 

 not an " equation division/' but a dissimilar distribution of 

 the "ids" of the spireme thread. In neither of these cases 

 is the first maturation mitosis of the heterotypical form. 

 Vom Rath's results were partly corroborated, partly modified, 

 by Wilcox (1896) for the spermatogenesis of Caloptenus 

 femur-rubrum and Cicada tibicen. The difference 

 between the two interpretations is that Wilcox found the 

 tetrad formed by conjugation of dyads, and reduction con- 

 sisted, therefore, not in the unequal distribution of sister 

 "ids" lyiug next each other in the spireme thread, but of 

 any " ids " indifferently from any part of the spireme thread. 

 Paulmier (1899), in Auasa, described the formation of the 

 tetrads more in the fashion described for the Copepods by 

 Riickert and Haecker, except that there is no spireme stage, 

 and his first maturation division is unequal, owing to the 

 manner in which the tetrad groups are placed on the spindle, 

 separation taking place in the original transverse plane. The 

 second division is an equal division, the separation being 

 effected along the original longitudinal plane of the tetrad. 

 It is to be noticed that his tetrads are not composed of four 

 separate elements, but are compound bodies, the elements of 

 which are condensed into a homogeneous mass. Riickert 

 (1894) and Haecker (1892-3) examined a considerable series 

 of Copepods. They found the earlier stages to differ in the 

 various forms, but the end result was always the same, 

 namely, a condensation of the elements into tetrad groups. 

 The early stages differed according as the split of the primary 

 rod was complete or incomplete at one or both ends, the 

 result being the formation of double rods, angles, or rings. 



Among the Copepods the case of Cyclops brevicornis 

 (Haecker, 1895) recjuires special mention. The splitting was 



