spermatogenesis 48 1 



fore describe in detiiil one species, Entilia sinuata, and then men- 

 tion the chief points of interest in the other species. 



Entiha sinuata 



This form was found in September, at Woods Hole, on the 

 leaves of the Golden Glow, and later near Philadelphia, on the 

 wild sunflower. 



The resting spermatogonia stain very lightly, as there are only a 

 few basichromatin granules in the midst of much scattered oxy- 

 chromatin (Fig. i). When the cell is preparing for division, a 

 heavy, rather darkly-staining spireme is formed with the chroma- 

 tin aggregated at regular intervals along the linin (Fig. 2). A 

 longitudinal split appears in this spireme, a slight indication of 

 which can be seen in Fig. 2. The chromatin next becomes con- 

 densed and segmented, but these segments still retain their linin 

 connections. The longitudinal split in each segment is also very 

 conspicuous at this stage (Fig. 3). Condensation of the segments 

 continues, there being first an elimination of the longitudinal split 

 (Fig. 4), and then a shortening of the segments until they are about 

 twice as long as broad, the form which they have as they enter the 

 equatorial plate of the spindle (Fig. 5). They appear in the plate 

 with their longitudinal axis at right angles to the longitudinal axis 

 of the spindle and with the linin connections still intact. This 

 division, therefore, is a longitudinal division, separating each chro- 

 mosome into two parts along the line of the original longitudinal 

 split, which appeared in prophase. A lateral view of the spindle 

 in metakinesis also shows convincingly that this division is longi- 

 tudinal (Fig. 6). The number of chromosomes in the spermato- 

 gonial division is 21 but it is impossible to pick out the odd 

 chromosome. The chromosomes become so closely massed 

 together in anaphase (Fig. 7) that one cannot tell whether the 

 linin connections still remain intact, or the conjugation of chromo- 

 some pairs takes place here. By the time the cell division is com- 

 pleted, the new nuclear membrane has been formed, possibly as 

 Conklin ('02) has suggested, by the joining together of the linin 

 sheaths of the chromosomes after these have absorbed liquid from 

 the cytoplasm (Fig. 8). A linin connection joining the chromo- 



