10 



CAPT. C. F. U. MEEK ON THE 



In everj complex that I have studied I have found the same number of 

 chromosomes, and the same size and shape relationships. With the exception 

 of the heterotropic chromosome, the members of the complex can be 

 arranged in a graduated series of eight pairs, divisible into three groups, 

 small, large, and medium : there are three small pairs, of which two are 

 spherical and the third ovoid, three pairs of large rod-shaped chromosomes 

 bent slightly at the middle, and two pairs of medium chromosomes, which 

 usually appear as straight rods. The heterotropic chromosome is the fourth 

 largest in the complex, and is a straight or very slightly bent rod, recognizable 

 for the first time at this stage. By choosing metaphases where the 

 chromosomes overlap only to a small extent, and by making camera-lucida 

 drawings upon successive occasions and comparing results later, I have tried 

 to minimize the possibility of error in counting the number of chromosomes 

 present; this difficulty is not experienced in the metaphases of the 

 spermatocytes, where only half the spermatogonial number is found, and 

 where cells can be chosen in which no overlapping occurs. Plate 1. figs. 3 

 & 4 show polar views of the spermatogonial metaphase, the seventeen 

 chromosomes being arranged on the equatorial plate. 



Gerard has found seventeen chromosomes in the spermatogonial complex 

 of Stenobothrus biguttulus, and Davis's results in the case of S. curtipennis 

 agree with this. McClung in an early paper suggested that the number is 

 dependent on the family, and is a constant, but this has not been found to be 

 strictly true. I believe the number is constant for the genus, but not for a 

 larger subdivision of the animal kingdom. Since the number has been 

 found to vary in the Orthoptera, it is interesting to compare the results of 

 writers upon this subject. Sutton has found twenty-three chromosomes in 

 Brachystola magna, capable of being arranged in three small and eight large 

 pairs, with an odd or heterotropic chromosome ranking among the latter. 

 Davis has counted the same number in Arphia tenebrosa, Hippiscus tuberculatus, 

 Chortophaga viridifasciata, and Melanoplus femoratus. In the Locustid, 

 Steiroxys trilineata, he has found twenty-nine, and has shown that in all 

 cases the ordinary chromosomes can be arranged in pairs forming a graduated 

 series. McClung has observed thirty-three chromosomes in Xiphidium 

 fasciatum ; and Nadine Nowlin has counted twenty-three in Melanoplus 

 bivittatus. When working upon crickets, Baumgartner found twenty-nine 

 in Gryllus assimilis and twenty-one in G. domesticus. 



The chromosomes, after placing themselves on the spindle, divide 

 longitudinally, and their halves pass to opposite poles ; the division of the 

 heterotropic chromosome is longitudinal, but occurs often at a later stage, 

 when the ordinary chromosomes have begun to move apart : an example of 

 the secondary spermatogonial telophase in shown on Plate 1. fig. 5. On 

 reaching the poles the chromosomes elongate and appear to lose their 

 affinity for the iron hsematoxylin : as the nuclear membrane reforms, they 



