1904.] NATURAL SCIENCES OF PHILADELPHIA. 213 



spindle (p^ and e). Figure 7 is a somatic cell containing 6 chromo- 

 somes. Six have also been counted several times in the first segmenta- 

 tion-division. That the second maturation-division of the chromo- 

 somes is longitudinal like the first one is evident from the form of the 

 chromosomes and from the pairs seen at a and h in fig. 10. Figure 

 1 1 shows the second polar body separating from the egg. 



Spermatogenesis. — ^As in the case of the ovaries, the testes should 

 be studied in summer after laying-time, in order to follow the develop- 

 ment of the spermatogonia, but occasional divisions of spermatogonia 

 and both spermatocyte-di visions may be observed in material pre- 

 served at any time during the autumn and winter. My best material 

 was fixed about the first of December. PI. XV, fig. 15, shows a part 

 of the section of a testis which contained dividing spermatogonia (a) , 

 both maturation-divisions (e and /), spermatids in all stages {g,h, i, k, 

 I), and ripe spermatozoa. In this animal the number of chromosomes 

 in the maturation-divisions was 4, in the spermatogonia 8. In several 

 others only 3 were found in the spermatocytes (figs. 20 and 22). Vari- 

 ous phases of the first maturation-division are showii in figs. 16-21 

 and of the second in figs. 22 and 23. The form of the chromosomes 

 in all phases of both divisions is the same, a Y-shape, easily distinguish- 

 able from the V-shaped and U-shaped chromosomes of the spermato- 

 gonia and somatic cells. There is no evidence of a transverse, or 

 reducing, division. In an anaphase (figs. 20 and 22), each daughter 

 chromosome appears to be drawn toward the pole of the spindle by a 

 single fiber attached to the stem of the Y. The spindle is composed of 

 very few fibers, and neither centrosomes nor asters have been demon- 

 strated. The spermatocytes before division appear as in fig. 15, d, 

 and nothing corresponding to the synapsis stage described by various 

 authors has been found. The spermatogonia in both resting and 

 division-stages closely resemble the so-called embryonic or paren- 

 chyma cells which are scattered through the planarian body and play 

 a conspicuous role in regeneration (fig. 15, a). 



Figs. 24—32 show^ various stages in the development of the sperma- 

 tozoon. The nucleus of the spermatid contracts, forming a small ball 

 of nuclear material which stains deeply and uniformly (figs. 24r-27, a). 

 This concentrated nucleus gradually elongates (figs. 27, b-29), and 

 finally leaves the cytoplasm tail first (figs. 15 and 29). Many empty 

 spermatid cells are shown in fig. 15; n. The spermatozoon appears to 

 be formed wholly from the nucleus of the spermatid, and stains like 

 chromatin throughout. The spermatozoa in the oviduct near the 

 ovary have a knob-like appendage near the anterior end (fig. 32) 



