SPERMATOGENESIS OF AMERICAN CRAYFISH 597 



double filaments resulting from this union correspond in some 

 cases to two chromosomes, in others to more chromosomes. 



Synapsis occurs in the forms of V's, parallel threads, rings, 

 spindles, crosses, twisted X's, etc. The figures that are most 

 common are spindle-like in which two chromosomes are united 

 at their two extremities and spread apart in the center. These 

 figures are called 'protetrads.' All in all Labbe found eighteen 

 protetrads. These form tetrads by becoming separated into 

 four large densely staining granules united by linin threads. The 

 eighteen tetrads therefore represent thirty-six chromosomes. 



The tetrads assume an equatorial position during the first 

 maturation division. In the metaphase stage of this division each 

 chromatin granule of the tetrad shows indications of a division 

 perpendicular to the plane of the equator. Labbe does not 

 regard this as a trace of the superficial division which occurred 

 in the spireme previous to tetrad formation, but regards it as a 

 second longitudinal division preparatory to the second matur- 

 ation stage. 



In the second maturation division the dyads arrange them- 

 selves in the equatorial plane of the spindle with their longi- 

 tudinal axes perpendicular to the equatorial plane. Since each 

 granule is divided into two, these dyads resemble microtetrads. 

 In the anaphase stage, the chromosomes are separated equa- 

 tionally and the enclosing nuclei of the telophase stage, therefore, 

 contain chromosomes that are microdyads, each microdyad 

 representing one-half of a chromosome. 



During the first maturation division, a chromatin nucleolus is 

 found within each cell, but in the second spermatocyte division 

 this does not seem to divide, but passes over entirely to one of the 

 spermatids. Therefore one-half of the spermatids contain this 

 nucleolus while the others are without it. 



In the same year ('04 b) Labbe also published another paper 

 in which he deals at greater length with the transformations of 

 the spermatozoa of Homarus vulgaris and Maja squinado. 



Keppen ('06), in a Russian paper on the spermatogenesis of 

 Astacus fluviatilis, lays special emphasis on the relation of the 

 spermatogonia and nutritive cells to the germinal epithelium. 



