Ivatliarine Foot and E. C. Strobell 21J)- 



forming a part of the original coil including four univalent chromosomes 

 or two bivalent chromosomes. The bivalent character is shown in the 

 lower of the two chromosomes by a clear space in the center, and a similar 

 clear space is shown in the l^ivalent chromosome just northeast of the 

 accessor!/ nucleolus. 



We have several intermediate stages between Photos. 115 and 116, Plate 

 VII, where the chromosomes are in the form of long thread-like loops, but 

 lack of space prevents our reproducing them. The bivalent character 

 of the chromosomes is clearly shown in many of the photographs. The 

 three rings in the upper part of Photo. 117, Plate VIII, show not only that 

 each ring is composed of two univalent chromosomes attached end to end, 

 but the longitudinal split of each is indicated, completing the transverse 

 and longitudinal markings typical of the tetrad. We may say that the 

 chromosomes of the prophase and metaphase are typical tetrads, for in 

 every preparation in which- the eleven chromosomes are shown, one or 

 more of them show beyond question both the longitudinal and transverse 

 markings. 



In Photo. 118, Plate VIII, at least five of the eleven chromosomes 

 show the transverse constriction, though in all these chromosomes the 

 longitudinal split is obscured. In Photo. 119 the tetrad character of at 

 least five of the chromosomes is almost schematically shown, the large 

 figure 8 shows not only the longitudinal split but a marked constriction 

 in each loop indicating the point of contact of the two univalent chromo- 

 somes. The small chromosome southwest of the figure 8 shows with 

 equal clearness its bivalent character and the longitudinal split, and the 

 three bivalent chromosomes north of the figure 8 admit of only one inter- 

 pretation. The fact that eleven bivalent chromosomes are typical of 

 the prophases of the first maturation spindle of AUolohophora is demon- 

 strated by the photographs of Plate VIII and the tetrad character of 

 these chromosomes is clearly shown. A good deal of scepticism has re- 

 cently been expressed as to the constancy of the number of the chromo- 

 somes in the first spindle, discrediting the great significance that has been 

 attached to this point. We would therefore accentuate the fact that in 

 every case where the chromosomes are so distributed as to admit of an 

 accurate count, we have not found a single exception to the number eleven 

 in the prophases and metaphase. Eods, rings and figures 8 are the 

 most common forms, though there are examples of the cross-shaped 

 chromosome which several investigators have demonstrated in other 

 forms. In Allolobophora an interpretation of their origin appears to 

 present no difficulties, they undoubtedly arise by a simple contraction 

 of a bivalent chromosome, i. e., two rod-shaped univalent chromosomes 



