1902.] NICHOLS — SPERMATOCxEXESIS ONISCUS ASELLUS LINN. 109 



Explanation o.^ the Plates. 



All of the figures, with the exception of i, 2 and 68, are camera drawings 

 made at the level of the microscope stage, and all except 3, 4a, 5, 6, 84-86, were 

 drawn with a Zeiss homogeneous immersion objective ^^, ocular No. 6, tube 

 length 100 mm. In those marked * the chromosomes are not all shown. 



Plate 

 XI 



Plate 

 XII 



Plate 

 XIII 



1. Free-hand drawing to illustrate the male reproductive organs of 



one side, a, d, c, lobes of the testis ; v, vas deferens; /, penis; 

 X, suspending tissue. 



2. Lobes of the testis in longitudinal section (semi-diagrammatic), a, 



d, c, as before ; spg.y spermatogonia ; / c, follicle cell. 



3. Longitudinal section of the vas deferens (Zeiss ocular 4, obj. AA). 



d, c, lobes of the testis. 

 \a. Small portion of the wall of the anterior region of the vas (oc. 6 



obj. D). 

 4b. Secretory cell from the anterior region of the vas. 



r 5. 



6. 

 7- 



*8 *c 



Plate 

 XIV 



Small portion oi a testis lobe in longitudinal section. /. c, follicle 

 cells; m. /., muscular layer (oc. 6, obj. D). 



Cells from the suspending tissue (^cf. Fig. i, x) (oc. 6, obj. D). 



(^) Spermatogonium in an early spireme stage; ncl, nucleolus. 

 Centrosomes beginning to divide, {b) Resting spermatogonium 

 with large masses of chromatin, probably beginning to degen- 

 erate. 

 9, 10. Later spireme stages. 



11. (a and f) Resting spermatogonia. {b) Spireme beginning to 

 segmeni. 



1 2. Equatorial plate in side view. 



13. («) Equatorial plate in pole view. (*3) Spermatocytic prophase, 

 171. /., muscle layer. 



14. Equatorial plate in side view, showing the longitudinal split in 

 the chromosomes. 



*I5. Metaphase. 



16, Approximate pole view of a stage similar to 15. 



17, Anaphase. 



18, Late anaphase. Mid-body. 



*I9, *20. Reconstruction of the daughter nuclei. In 20 the mid body 

 has migrated to the periphery. 



*2i. {a and b) Reconstruction of the daughter nuclei, (t) Degen- 

 erating spermatogonium. 



22, 23-28. Synapsis. 26. 1-16, chromosomes. 



27. Different forms of the chromosomes in the synapsis. 



29. Formation of the nuclear membrane. 



30. Resting spermatocyte, spg., spermatogonium. 



31. Irregular arrangement of the nuclear network, occasionally seen 

 juit before the formation of the nuclear membrane. 



