1904.] NATURAL SCIENCES OF PHILADELPHIA. 219 



Fig. 4. — Same with 4 cliromosomes (a part of one chromosome in next 

 section). 



Fig. 5, a and h. — Egg from section of a capsule before laying, showing second 

 maturation-spindle and 3 chromosomes, s = sperm. 



Fig. 6. — Same as above, showing first polar body and 3 chromosomes. 



Fig. 7. — Somatic cell from a regenerating piece of Planaria lugubris, showing 

 6 chromosomes. B. and L. ju-C. 



Fig. 8. Egg from a capsule before laying, stained with Schneider's aceto- 

 carmine. p^ = 1st polar body, p'^ = chromosomes of 2d polar body, 

 s = sperm, e = egg-chromosomes. B. and L. |-C. 



Fig. 9. — Similar egg with 6 egg-chromosomes (e) and 6 chromosomes for 

 the 2d polar body (p^). 



Fig. 10. — Egg from same capsule as 9, showing longitudinal division at a 

 and b. 



Fig. 11. — Similar egg showing 2d polar body (p^), sperm (s) and egg-chromo- 

 somes (e). 



Fig. 12. — Egg from capsule just laid showing pronuclei. 



Fig. 13. — Egg from capsule 3-4 hours after laying, showing pronuclei fused 

 but nucleoli distinct. 



Fig. 14a.- — Egg from a capsule 8-10 hours after laying, showing first seg- 

 mentation-spindle with 6 cliromosomes at each pole. 



Fig. 146. — Optical cross-section of polar plate, showing two cross-sections 

 of each of the 6 chromosomes. 



Figs. 33-35. — 2-celled, 4-celled and 8-celled stages from sections of capsules, 

 showing the peculiar relative positions of the blastomeres. Fig. 35 

 is a reconstruction from five sections. B. and L. |-C. 



Fig. 36. — Section of a 32(?)-celled stage, yolk-cells breaking down at x, x. 

 B. and L. J-C. 



Plate XIV, Fig. 15. — One-half of a cross-section of an unusually large testis. 

 a = dividing spermatogonium, b = small spermatagonium after di\i- 

 sion. c = resting spermatgonium. d = resting spermatocyte of the 

 first order, e = first maturation division. / = second maturation 

 division. g= young spermatids, /i, i. A; = spermatids in later stages. 

 I == spermatid apparently twice the usual size, m = spermatozoa. 

 n = empty spermatid cells. B. and L. ^-C. 



Figs. 16-21. — Various phases of first maturation divisions, showing 3 and 

 4 chromosomes. B. and L. rj— C. 



Figs. 22 and 23. — Second maturation division. 



Figs. 24-29. — Spermatids in various stages. 



Figs. 30-31. — Spermatozoa from the testis. 



Fig. 32. — Spermatozoon from the oviduct near the ovary. B. and L. xV~C. 



Plate XV, Fig. 37.— Section of a slightly later stage (64-celled)(?), showing an 

 irregular mass of blastomeres (b), a definite embryonic yolk-area (y') 

 and a region of disintegrating yolk-cells (a). B. and L. ^-C. 



Fig. 38. — Section of a still later stage, showing larger embryonic area con- 

 taining yolk-nuclei (i/), yolk-cells (i/), wandering blastomeres (6), 

 and the beginning of the embryonic pharynx (p'). Same magnif. 



Fig. 39. — Cross-section through the central cells (b) of an embryonic pharynx 

 (pi), well-developed, but not yet functional, c = muscle-cells, 

 yi = yolk-nucleus, bl. = blastomeres scattered in the yolk of the 

 embryonic area, e = flattened blastomere on the surface of embryo. 



Fig. 40. — Longitudinal-section through an embryonic pharynx of the same 

 age as 39. a = two of the 4 large surface cells bounding the lumen. 

 b = two of 4 central cells, c = muscle-cells, d = two of the 4 inner 

 lumen-cells, e = a blastomere partly on the surface of the embryo. 

 7j^ = yolk-nucleus. B. and L. ^C. 



Fig. 41. — Cross-section of the 4 inner lumen-cells of the embryo shown in 

 Fig. 39. 



Fig. 42. — Functional pharjmx, lumen open and yollv-cells entering. Same 

 magnif. 



