Plate III. 

 Hipitji talpoides. 



Hi, 22. Young spermatid. 



Hi, 23. Abnormal spermatid. 



Hi, 24. Development of mitochondrial ring and of the strands which will 



become the streamers of the middle-piece. 

 Hi, 25. (a) Differentiation of tail-capsule and decoloration of nucleus. 



(b) Pole view. 



Hi, 2G-2S. Development of tail-capsule, tube, ring and plug. In these 



figures the streamers are not shown. 

 Hi, 29. Elongation of the capsule. Condensation of x". Appearance of 



striations. 

 Hi, 30. a, Later stage, b, c and d, variations in the appearance of xl 



e and f, cross sections in the region of the nucleus and of x-. 

 Hi, 31. a, Stage very nearly the same as 29, but of somewhat different 



aspect, b, cross section of x-. 

 Hi, 32-34. Final stages in the development of the spermatid. 



Homarus vulgaris. 



Ho, 8. Spermatid before the formation of the tube. 



Ho, 9. (a) and (b). Cross sections showing manner of formation of tube. 



(c) In the region of the middle-piece, showing the centrosome and 

 beginnings of the three streamers. 



Ho, 10. Spermatid after formation of the tube. 



Eupagurus longicarpus. 



E, 1-5. Development of the spermatid. 



Palaemonetes sp. 



Development of the spermatid. 



P, 1-3. Three nuclei of the syncytium. 2 is disintegrating. 3. Condensa- 

 tion of mitochondria around transformed nucleus. 

 P, 4. Formation of tail. Two centrosomes and an axial filament are 



evident. 

 P, 5. Cup-shaped nucleus and single centrosome. The tail has elongated. 

 P, 6. (a) Lens-shaped nucleus. Beaded axial filament, (b) Pole view. 

 P, 7. Abnormal spermatid. 



Talorchestia longicornis. 



T. 19-22. Secretory cells from the vasa deferentia. 



T, 23. Testis and vas. go., spermatogonia, cy., spermatocytes. 



Idotea irrorata. 



I, 2G-27. Secretory cells from the vas. 



I, 28. One of the three testis lobes, showing the lateral arrangement of 

 the developing germ-cell. 



Oniscus asellus Linn. 



O, G. Secretory cell from the vas. A small portion only of nuclear net- 

 work shown. 



