MATURATION OF OVUM IN ECHINUS ESCULENTUS. 207 



partly reconstrncted between the divisions, and the longi- 

 tudinal cleft is lost sight of, to reappear in the second 

 division either by re-establishment of the old or by a 

 new longitudinal splitting. Kingsbury was able to trace 

 the longitudinal cleft directly into the second division, 

 owing to the fact that the nucleus is not so far recon- 

 structed. More recently (July, 1900) Janssens described 

 the phases in Triton, and took the further step of inter- 

 preting the process in exactly the same terms as 

 Gregoire in lilies. Flemraing (1887), in his first paper, 

 described tetrads, but regarded them as abnormal. Vom 

 Rath (1893) redescribed these bodies as normal appearances, 

 but his results were not maintained by Moves (1896), who 

 failed to find the least evidence of tetrads in amphibian 

 spermatogenesis, tliongh he, in a short paper, described 

 tetradal figures as an abnormality in the early oocytes. 



Amphibian oogenesis has been attacked by Fick (1893) 

 and Born (1894), and Carnoy and Le Brun (1899). Practi- 

 cally identical figures are given by all three, but the later 

 authors give much more complete details, and offer a new 

 interpretation. They describe the chromosomes as condens- 

 ing after some intermediate phases into short rods. These 

 are complex structures formed by the fusion of a considerable 

 number of separate elements. These short rods, or rather 

 blocks, place themselves in the equatorial plane of the spindle 

 in a circle round its periphery, and orient themselves so as to 

 be placed with their thicker and larger ends on the spindle, 

 the other end being directed outwards. Once installed in 

 this position, the chromosomes go thi'ough varied movements 

 during which they submit to a double longitudinal splitting. 

 The one is effected in the equatorial plane, the other in the 

 axis of the spindle and perpendicular to the first. The 

 equatorial division shows itself first and begins in the large 

 part attached to the spindle, rising insensibly into the stalk. 

 The second occurs later, and begins at the summit of the 

 stalk, descending by degrees till a kind of tetrad is formed. 

 Further complicated changes are described, which result in 



