Plate 1. 



The effect of the parasites on their host. Parasites of the parasites. 



(Figs. 1 — 2 1 refer to Inaehus scorpio.) 



ov ovary, p copulatory style. S scar of Sacculina. t testis. 



Fig. 1. Adolescent female, dorsal view. Nat. size. 



Fig. 2. Abdomen of Fig. 1, ventral view. X 2. 



Fig. 3. Adult female, dorsal view. Nat. size. 



Fig. 4. Abdomen of 3, ventral view. X 2. 



Fig. 5. Abdomen of adult infected female, ventral view. X 2. 



Fig. 6. High male, dorsal view. Nat. size. 



Fig. 7. Middle male, ditto. 



Fig. 8. Low male, ditto. 



Fig. 9. Infected male, dorsal view. Nat. size. 



Pig. 10. Same as Fig. 9, but more modified. Nat. size. 



Fig. 11 and 12. Abdomina of infected males, ventral view. X 2. 



Fig. 13. Abdomen of normal uninfected male, ventral view. X 2. 



Fi°\ 14. Infected male of I. scorpio, modified into perfect hermaphrodite form. Dorsal view. Nat. size. 



Fig. 15. Abdomen of Fig. 14, ventral view. X 2. 



Fig. 16. Infected male, modified into perfect hermaphrodite. Dorsal view. Nat. size. 



Fig. 17. Abdomen of Fig. 16, ventral view. X 2. _ 



Fig. 18. Hermaphrodite crab, found in nature, not bearing any signs of Sacculina. Dorsal view. Nat. size. 



Fig. 19. Abdomen of Fig. 18, ventral view. X 2. 



Fig. 20. Section through hermaphrodite gonads of recovered crab of type figured in Fags. 14—17. X 45. 



Fig. 20a. Enlarged drawing of a piece of hermaphrodite gonad, showing ova and sperm lying together in 



same tube. X 325. _ 



Fi°\ 21. Male, experimentally recovered from Sacculina in Aquarium, which formed hermaphrodite gonad. 



Nat. size. Ventral view. 



art dorsal artery, b.c brood pouch, eg colleteric gland, cl mantle opening, h external chitin. co nerve 

 cord, end endoderm. ect ectoderm. E eye. gn ganglion, h heart. m mantle, mes mesentery, n phago- 

 cytic cells, ov ovary, op opening of spermatheca. o.t ovotestis. pr proboscis. ri ring of attachment. 

 sp.il/. spermatheca. t testis, visc.mass visceral mass. 



Fig. 22. Cryptoniscus larva of Danalia curvata, male stage. Dorsal view. X 40. 



Fig. 23. Same as Fig. 22, ventral view. X 40. 



Fig. 24. Transverse section through hinder part of thorax of Cryptoniscus larva to show testis. X 175. 



Fig. 24a. Spermatozoa from testis of larva. X 1300. 



Fig. 25. Transverse section through hinder part of thorax of Cryptoniscus larva, some time after fixation. 

 The phagocytic cells (n) absorb remains of testis. X 17 5. 



Fig. 26. Transverse section through anterior part of thorax of Cryptoniscus figured Fig. 25, to show ovary (ov). 

 X 175. 



Fig. 27. Whole view from side of Danalia currata shortly after fixation and loss of larval appendages. X 80. 



Fig. 27a. Optical section from dorsal view of Danalia curvata at same stage as Fig. 27, to show great deve- 

 lopment of phagocytic cells (n). X 175. 



Fig. 28. Transverse section through middle of thorax at about same stage as Fig. 27. X 175. 



Fig. 29. Transverse section through thorax of Danalia curvata, when nearly adult. X 40. 



Fig. 29a. Spermatozoa from spermatheca of Fig. 8. X 1300. 



Fig. 30. Inaehus scorpio, Q, bearing on abdomen two specimens of Sacculina negketa and one specimen 

 of Danalia currata, on which are two Cryptoniscus larvae fertilizing it. X 2. 



Fig. 31. Galathea dispersa with Lernaeodiscus galathcae on abdomen. Ventral view. X 4. 



Fig. 32. Galathea dispersa with Danalia ypsUon on abdomen. Ventral view. X 4. 



Fig. 33. Lernaeodiscus galatheae, viewed by transparency in situ on its host. X 12. 



Fig. 34. Lernaeodiscus galatheae, lateral (right) view, mantle cut away to show visceral mass, position of 

 organs and mesentery. X 12. 



