75 The effect of the Parasites ori their Hoste. 



This crab therefore makes the fifth. recovered individuai with hermaphrodite gonads 

 found so far, and like ali the others it showed a perfect external hemaphroditism as well. 

 This individuai is figured in Piate 7 fig. 21. The copulatory styles (p) were very small, as 

 were also the other appendages. 



It appears therefore fairly certain that only those crabs with perfect external herma- 

 phroditism, i. e. perfectly modified males, are capable of regenerating an hermaphrodite gland. 



3. The cellular origin of the regenerate d gonad. 



I have spoken of the gonads of these hermaphrodites as having been practically eradi- 

 cated; it is therefore naturai to enquire how and from what cells the hermaphrodite gonad is 

 regenerated. The answer to this question must be found in the condition of the gonads of 

 those infected crabs described in Paragraph C, which were externally perfect hermaphrodites, 

 because these crabs, on recovery, evidently furnish the material for the animals whicli are 

 hermaphrodite externally and internally. I have stated in Paragraph C that in the great 

 majority of these crabs no trace of a gonad could be detected, but that in three specimens 

 the degenerate remains of a testis could be detected. Sections through these degenerate remains 

 showed an entire absence of spermatozoa, the tubes being simply lined with undifferentiated 

 germinai cells. The vesiculae seminales contained a clear fluid but no sexual elements. It 

 can hardly be doubted therefore that the regeneration of the hermaphrodite gonad takes place 

 from the small shreds of testicular epithelium which to a varying extent probably persist in 

 ali these crabs, but which in the majority of cases are so small and fragmentary as easily 

 to escape detection. 



3. The Case of Eriphia spinifrons. 



A. The simultaneous parasitism of Entoniscidae and Rhizocephala. 



In this section, through the kindness of Dr. G. Duncker, I am able to bring forward 

 a very complete confirmation of a highly remarkable observation made originally by Fritz 

 MtJLLER (Entoniscus porcellanae, eine neue Schmarotzerassel. in: Arch. Naturg. 18. Bd. p. 10), 

 and afterwards adopted and extended by Giard & Bonnièr (Contributions à l'étude des Bopy- 

 riens. in: Trav. Inst. Z. Lille Tome 5). This observation concerns the simultaneous parasitism 

 in a crab of an Entoniscid 1 ) and a Rhizocephalon, and constitutes perhaps one of the most 

 mysterious facts in parasitology. Fritz Muller observed that on 1000 Porcellana crabs there 

 were 84 specimens of the PJiizocephalon Lernaeodiscus porcellanae and 49 of Entoniscus por- 



l ) The Entoniscidae are a family of the Bopyrid Isopods. The parasite enters the branchial chamber of the 

 crab and finally in the adult stage becomes invaginated into the thoracic body cavity, occupying a large space with 

 its hugely developed ovary. 



