122 bulletin: museum of comparative zoology. 



apart as the entire diameter of the spindle (cf. Plate 2, Fig. 18, and 

 Fig. L, p. 77). I believe the facts can be better explained on the 

 assumption that there is a marked attraction between the components 

 of each pair, which results under ordinary circumstances in their lying 

 close together, but would not prevent their being temporarily separated 

 by various factors, such as the crowding of neighboring chromosomes, 

 and the like. 



McClung (:05) has held that there may be a still closer association 

 of the chromosomes in the spermatogonia. He asserts that in several 

 Orthoptera a "precocious conjugation" of certain autosomes may 

 occur at this early stage. The rod-shaped autosomes become joined 

 end to end forming a U-shaped element, to the center of which the 

 mantle fibers become attached. I have no material from any of the 

 species in which McClung found such precocious conjugation, with 

 the exception of Chortophaga viridifasciata, but in this species I have 

 been unable to find any e\'idence of conjugation in the spermatogonia. 

 In fact, in my preparations of Chortophaga the chromosomes are, if 

 anything, more widely separated than in most species. However, 

 I have been able to find very few cells which afford a good view of the 

 equatorial plate and these are all among the earlier generations. 

 It is probable that in the later generations, owing to the decrease in 

 the size of the cells, the chromosomes become more closely crowded 

 together. It is possible" that in some cases McClung has mistaken a 

 univalent for a bivalent autosome. Apparently one of his chief 

 reasons for considering certain autosomes in the spermatogonia to 

 be bivalent is the fact that they are U-shaped — having the mantle 

 fibers attached at the apex, and exhibit the so-called heterot}^ical 

 form of mitosis. In Stenobothrus six of the spermatogonial auto- 

 somes show these characteristics, and yet it is very certain that they 

 are all univalent. 



3. Synapsis. 



It is not my intention to attempt a complete review of the already 

 enormous literature on this stage in the development of the germ cells, 

 but only to' consider the more important results of some of the more 

 recent investigations. The term synapsis was first applied by Moore 

 ('95) to a stage in the early growth period when the chromatin is 

 massed at one side of the nucleus, during which, as he believed, the 

 reduction in the number of chromosomes takes place. Inasmuch as 

 it has since been shown that in many cases no such contraction of the 



