iqi2] YAMANOUCHI—CUTLERIA 469 



(fig. 151), but sooner or later the cell begins to elongate upward 

 until its length becomes three times its width, the top being slightly 

 swollen and the base narrowed. The nucleus lies either in the center 

 or a little above the middle of the cell. The cytoplasm is full of 

 vacuoles of various sizes, and plastids are quite numerous. 



The nucleus in the resting condition contains a moderate amount 

 of chromatin network and a nucleolus. The network is composed 

 of very small chromatin knots and irregular fibrils (fig. 152); the 

 proportionate amounts of the knots and fibrils seem to interchange 

 at this stage (fig. 153). In iron-hematoxylin preparations dark 

 kinoplasm surrounds the nucleus (figs. 151, 152). The amount of 

 the chromatin gradually increases and the general tendency is 

 for the broken fibrils to become thicker and continuous, transform- 

 ing the knots into the fibrils (fig. 154). At this time, a single 

 (figs. 154, 158) or double (figs. 155, 157) centrosome-like structure 

 with radiations is recognizable at the poles. 



Stronger and more continuous threads are then established by 

 the rearrangement of the knots and fibrils. The chromatin net- 



work, which is composed of a number of broken threads of various 

 lengths and thicknesses, now entirely devoid of former knots, is 

 not very great in amount. For a while the broken threads are 

 seen running for quite a distance either close to the membrane or 

 traversing the cavity (fig. 159, 160). Then the threads gradually 

 become more and more uniform in thickness and are transformed 

 into somewhat regularly arranged loops, centered at a certain 

 part of the cavity ^fig- 161). This transformation represents the 

 beginning of the synaptic stage. 



This bunch of loops may be in regular arrangement (fig. 162) or 

 adhering at the base to the membrane and diverging upward so that 

 each loop passes along the membrane (fig. 164); or often each loop 

 of the bunch differs in compactness of structure, and consequently 

 some loops are short while others extend for some distance (fig. 165). 

 In any event, a cross-section at these stages shows that the number 

 of the cut ends of the arms of all the loops is about 48 (fig. 166). 

 These loops now shorten considerably (fig. 167) and some of them 

 are soon detached from the main group and form paired chromo- 

 somes (figs. 168, 169), and finally there are established 24 bivalent 



