206 THOMAS H. BRYCK. 



Elasmobrancli spermatogenesis, adopted this explanation 

 of his figures. Gregoire (1899), describing the stages 

 in lilies, and Strasburger in his recent work, from a 

 careful examination of the prophase in a large number of 

 plant forms, absolutely decide against the idea of the bend- 

 ing up of the ring. In Echinus, where no ring is seen at 

 any time, the explanation is easier and more direct, and the 

 facts decide conclusively against such an interpretation. 

 Strasburger, in addition to examining a large series of cases, 

 reviews the results of other observers, and comes to the 

 general result that all the processes can be referred to one 

 type, namely, (1) As the result of the primary longitudinal 

 cleavage of the chromatin thread, two rods, wavy or 

 curved, are formed. These straighten and ultimately 

 shorten down into stout rods. In shortening, various adhe- 

 sions and twistings may take place, so as to form rings or 

 twisted threads. (2) According to the position assumed by 

 these various figures on the spindle, the character of the 

 resulting metaphase figures depends, (a) If the chromo- 

 somes are placed radially in the form of two rods side by side, 

 they are drawn apart in the plane of the first cleavage, and 

 at the same time a second slit is effected from the free end 

 inwards. The result is the formation of V-shaped daughter 

 chromosomes, which in the anaphase break apart at the apex 

 to complete the second longitudinal cleft. (h) If placed 

 tangentially the result depends on the point of attachment 

 of the " zugfasern," but invariably as the limbs are drawn 

 apart, a second longitudinal cleavage reveals itself, and two 

 daughter Vs are formed. The first type {a) is exactly what 

 I have described in Echinus; the second form {h) is exactly 

 that described in amphibians. 



Flemming (in 1887), and Moves (189G) in Salamander, 

 McGregor (1899) in Amphiuma, Kingsbury (1899) in Desnio- 

 gnathus, give us conclusions in the main identical. All 

 describe and figure a second longitudinal cleavage of 

 the chromosomes in the dyaster stage, and this cleavage 

 is preparatory to the second division. Tlie nucleus is 



