708 C. E. McCLUNG 



rate before the mid period of the movement and so appear as V's 

 instead of as extended rods. 



While Mecostethus presents an extreme case^ it is not at all 

 unique and many species show one or more of the same type of 

 rods in metaphase. Wherever found they show a fiber attach- 

 ment at the middle point and pass from the rod shape, through 

 that of the cross, to the rod again, but now extended in the spindle 

 axis and with an approximation of homologous chromatids instead 

 of sister elements. This approximation is retained, in most cases, 

 until the complete separation of the metaphase chromosomes, 

 whereupon the chromatids spring apart and move toward the 

 poles as V's. Obviously this is an equation division. 



2. The V-shaped tetrad. As has already been stated the V- 

 shaped chromosomes of the metaphase represents merely the 

 rod type bent at the point of fiber attachment, so that the apex 

 is directed toward the spindle axis. Such forms are rarely repro- 

 duced in the figures of investigators for the reason that polar 

 views, from which point only they are visible, are not given. At- 

 tention has already been directed to this neglect. Mecostethus 

 is the most striking instance of the occurrence of such chromo- 

 somes, but, as may be noted in plates accompanying this paper, 

 they are common in Hippiscus, Tropidolophus, Hesperotettix and 

 Mestobregma. Robertson shows in a series of complexes the 

 forms of the individual chromosomes in the first spermatocyte 

 metaphase, mainly in polar view, and here it is seen that the ones 

 numbered 3, 4, 6, 7, 8 and 10 may appear as V's. If not in this 

 form they are rings viewed laterally. V-shaped chromosomes may 

 only with some difficulty be distinguished from rods or rings. En 

 face they are again similar to these forms, and all of them resem- 

 ble the crosses. These facts are very suggestive of the fundamen- 

 tal unity of form underlying all the diverse shapes present in the 

 first spermatocyte. In actual division the V's are not to be 

 distinguished from the rods. 



3. The cross-shopped tetrad. While V's are a feature of the polar 

 aspect of the metaphase figure, crosses appear only in lateral 

 views, and then only when the chromosomes are regarded eii face. 

 While simple crosses occur, other chromosomes may present 



