The celliuar elemeuts of the Ovary of Platyphylax designatus Walk. 223 



breaking up of tlie paired cliromosomes in the nurse-cell nuclei, that 

 we will speak of it at this place. The formation of the dyads, of 

 their assuming a dumb-bell shape, and finally the tetrad formation, 

 is very similar in the nurse-cells of Platyphylax to what Giaedixa (8) 

 found in the same cells 'of Dytiscus. G-rünbeeg (12) also notices 

 for Pleris, that the tetrads in the nurse-cell nuclei, break up into 

 many small granules which finally fill the nucleus. In about the 

 middle of the tubule each oöcyte has lying distal to it, or slightly 

 at its side, a group of nurse-cells; in the nucleus of both kinds of 

 cells there is, besides a large achromatin nucleolus, a number of 

 small achromatin masses, remains of earlier threads, in each of 

 which lies a pair of chromosomes. In the youngest group we have 

 drawn (Fig. 29) the oöcyte is larger than any nurse-cell, but the 

 structure of its nucleus is the same. As in all the groups the oöcyte 

 nucleus remains unchanged (Figs. 29 to 33 oo), we need not speak 

 of it but confine ourselves to that of the nurse-cells. A little older 

 stage shows, that while there are some distinct paired chromosomes 

 present, in the place of many of them there is an apparent tetrad 

 formation (Fig. 30). Some of these are undoubtedly tetrads, but in 

 others the appearance is due to the chromosomes each having the 

 shape of a dumb-bell with a thin, beut handle, which is not always 

 Seen. A slightly older cell (Fig. 31) shows about the same structure, 

 but we notice, that instead of paired rods or of tetrads, there are 

 some groups of five or more small chromatin granules which have come 

 from the breaking up of the paired chromosomes. Still a little later 

 (Fig. 32) these paired chromosomes and tetrads entirely disappear, 

 and in their place, we find small groups of chromatin granules, not 

 of five or six, but more in number. Each group is entirely distinct 

 from the others. The granules then spread throughout the nucleus 

 until they occupy a position similar to what we find in the oldest 

 nurse cell (Fig. 33) of this tubule; here the groups have become 

 entirely lost and the chromatin granules spread throughout the nucleus 

 GiARDiNA (8), Grüxberg (12). They have increased very much in 

 number, but only in part fill the nucleus, leaving in it large, empty 

 Spaces. As we have already said the first of these granules come 

 from a breaking up of the paired chromosomes; whether the others 

 come from those already formed or not we do not know. The 

 number seen in older nurse-cell nuclei is too great to all be derived 

 from a breaking up, or a Separation, of the paired chromosomes. 

 In the oldest nurse-cell nucleus of the next stage, ovary D, (Fig. 36) 



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