182 



SCIENCE 



[N. S. Vol. XLI. No. 1048 



but as they mature their walls thicken and beeome 

 differentiated into a thick inner and a thin outer 

 layer. At the instant of discharge the inner layer 

 swells and becomes gelatinous, the outer layer is 

 irregularly ruptured, and the egg is forced 

 through the opening, thus formed, sometimes to a 

 distance of 0.24 mm. In escaping the egg is still 

 enclosed by the gelatinous inner layer, but is soon 

 set free by the solution of this layer. 



'The observed facts indicate that the force 

 utilized in discharging the eggs is obtained solely 

 by the swelling of the inner layer with the con- 

 traction of the stretched outer layer of the 

 oogonium wall. 



Both at Beaufort, N. C, and at Naples, about 

 65-75 per cent, of aU the eggs of each crop were 

 discharged within a single hour of a siugle day, 

 beginning at about the time of the first observable 

 traces of dawn. 



The swelling of the inner layer of the oogonial 

 wall, with the resultant discharge, did not occur 

 in eggs that were killed by heat, cold or chem- 

 icals, and was practically or entirely prevented by 

 anything that interfered with the life conditions. 

 It could not be initiated by any means before the 

 usual time for discharge, but, as the usual time 

 approached, seemed slightly accelerated by trans- 

 fer from a moist dish to sea water. 



The above facts seem to indicate that the swell- 

 ing of the inner layer of the oogonial wall is under 

 the direct control of the protoplasm, or that it is 

 accomplished by means of enzymes formed by 

 the protoplasm and affected by the same condi- 

 tions that affect the living substance. Of these 

 two possibilities, the latter seems more probable. 



Cell Division and the Formation of Colonies of 



Volvox: E. A. Haspee. 



The planes of the first two divisions of the 

 mother cell of the young colony intersect at right 

 angles. The plane of the third division lies so as 

 to form the well-known cross figure. The factors 

 determining this deviation from Sach's principle 

 of rectangular intersection are associated with the 

 surface tension developed in. a plate made by 

 successive bipartition of cells, and lead to the 

 further incurving of the plate and formation of 

 the globular colony. 



Prochromosomes in Synapsis: C. A. Darling. 



The work on prochromosomes by Eosenberg, 

 Overton and others has suggested the possibility 

 that some cells might be found the study of which 

 would considerably increase our knowledge con- 

 cerning the behavior of the chromosomes in synap- 



sis and reduction. Such cells have been found in 

 the Norway Maple Acer platanoides. 



In the so-called resting stage of the nucleus of 

 the pollen mother cell in this species are 26 defi- 

 nite bodies corresponding in number to the 26 

 chromosomes found in the vegetative cells at the 

 time of division; most of these bodies, or pro- 

 chromosomes, are distributed about the periphery 

 of the nucleus, but a few are to be found lying 

 close to or against the nucleus. Upon staining 

 with safranin, gentian-violet and Orange G., these 

 26 prochromosomes are stained blue and the nu- 

 cleolus red, so that the two are readily distin- 

 guished. At this stage the linin threads take the 

 stain only sparingly. At least some of these 

 threads appear to be attached to the prochromo- 

 somes; in some cases the threads are connected, 

 forming a sort of net with nodes or thickenings; 

 these nodes do not take the gentian-violet stain 

 and are not definite bodies like the prochromo- 

 somes. 



The prochromosomes are noticeably arranged in 

 pairs; in some cases the two are separated by at 

 least twice their own width, while in other pairs 

 they almost touch each other; in no case do they 

 appear to be connected. The prochromosomes vary 

 somewhat in size, but so far as observations go 

 the individuals of a pair appear to be equal. 



As the period of synapsis approaches, the 

 threads become more conspicuous and take the 

 gentian-violet stain more readily; the prochromo- 

 somes still retaining their definite individuality 

 appear to come closer together. The beginniug of 

 synapsis is indicated by the contents of the nu- 

 cleus being drawn toward the nucleolus and col- 

 lecting at one side of the nuclear cavity. The 

 whole network of threads and prochromosomes be- 

 comes more or less massed; only in rare eases do 

 any of the threads appear to lie parallel. 



In complete synapsis only a few threads are 

 distinguishable, especially those extending out 

 from the synaptic knot. The prochromosomes, 

 however, are still very apparent; in most pairs- 

 the members appear to be in contact with each 

 other, although some are still separated. As 

 growth proceeds the threads which extend outside 

 of the knot beeome thicker and contain more 

 chromatin, as shown by their staining reaction. 

 These threads soon become double, the evidence 

 indicating that this is due to a longitudinal split- 

 ting of a single thread rather than to the parallel 

 arrangement of two separate threads. Apparently 

 each of these thick threads is formed by the grad- 

 ual flowing out of the contents of the prochromo- 



