300 Morphologie der Zellen, Gewebe und Organe. 



technique and precautions against error are fully described. Starting from several 

 species of the genus Stenobothrus (Acridiidae), he finds that, apart from the hetero- 

 tropic cliromosome, all the ordinary chromosomes in both somatic and spermato- 

 cyte divisions have a common diameter (0.83 fi) through their length, and that 

 the eight ordinary chromosomes of the reduced (haploid) complex have lengths 

 which fall into a series in arithmetical progression, of which the difference bet- 

 ween consecutive terms is half that of the diameter of the rod (0.41 (i). In all 

 species of Stenobothrus studied, the five smallest chromosomes are consecutive 

 members of this series, with lengths 1.7, 2.1, 2.5, 2.9, 3.3 ,«. The three larger 

 chromosomes are not consecutive, and differ in different species, but have lengths 

 corresponding with members of the arithmetical series mentioned. The total vo- 

 lume of the ordinary chromosomes is the same in spermatogonial and primary 

 spermatocyte mitoses; in general it is halved at each division, and increases to 

 the füll amount in the resting stage of the nucleus. This is presumably the pur- 

 pose of the dissociation of the chromosomes into granules in the resting stage; 

 each granule splits when its volume has been increased, and condensation on both 

 sides of this split results in the formation of a double chromatin rod, i. e. a cliro- 

 mosome ready for longitudinal division. In the metaphase of the first spermatocyte 

 division, the chromosomes (in reduced i. e. haploid number) consist each of four 

 rods instead of two, the chromosomes having become associated in pairs, and 

 since there is no resting phase between the divisions, the spermatids contain one 

 fourtli of the volume of chromatin found in the spermatogonial metaphase, or 

 one half of that in the spermatogonial anaphase. Since the heterotropic chromo- 

 some divides only once in the maturation divisions instead of twice, it does not 

 need to become resolved into granules in the growth-phase, for it has already 

 attained its füll size; hence the fact that it remains as a compact body at this 

 stage in all species in which it has been observed. 



Having found that the ordinary chromosomes of Stenobothrus have a constant 

 diameter, and lengths which are always simple multiples of half that diameter, 

 the author compares with them, first, chromosomes of Orthoptera of other families, 

 and then those of Homo, Triton, Hclix. J.umlricus and Ascaris, and faids that in 

 each of these genera the chromosomes have the same diameter (0.83 jti), and 

 often have lengths which are simple multiples of the radius, i. e., in each case 

 some at least of the chromosomes fall into the same arithmetical series as regards 

 length which w^as found in Stenobothrus. In Linens (Nemertinea), Echinus, Astcrias, 

 Alcyonium, the chromosome width is half that of the higher phyla (0.42 ft), "and 

 the lengths possibly foUow the same series; in the Protozoa Monocystis, Englena, 

 Paramaecium the diameter is 0.21 fi, i. e. half that of the lower Metazoan phyla. 



In conclusion, it is suggested that primitive chromatin particles in the lowest 

 organisms became converted into chromosomes (rods) by purely linear growth; 

 this growth is not allways the same, so that chromosomes of varying lengths 

 appeared. When the rods have attained a maximum length (possibly conditioned 

 by the spindle mechanism), they conjugate in fours, giving rods of twice the 

 previous diameter, and segment into spherical chromosomes of the new width. 

 " They are then prepared to enter upon a new course of linear growth, accompanying 

 further evolutionary development, and in the higher phyla have repeated this 

 process, so that the chromosome rods have attained four times the original width. 

 The heterotropic chromosome, when present, has greater width which is not con- 

 stant; it cannot tlierefore belong to the general series. 



Doncaster (Cambridge). 



