TERATOLOGY AND PATHOLOGY. 



201 



Tlie p3clinogonidaii which thus infests the Syncorync c.vimir/, and probably also that of other 

 Corynidec, appears to be the PhovichUiduim coccinetim of Johnston. There can, I think, be 

 little doubt that the eggs of the parent Phocivhi- 

 lid'uim arc swallowed by some of the hydranths 



of the colony, and thus reach the somatic cavity, pj^ yj 



from which they gain access to the interior of 

 a young bud, which, under ordinary circum- 

 stances, would have become a hydranth-bearing 

 branch, but which now becomes arrested by the 

 developing parasite, and changed into a recep- 

 tacle for its protection, in a way which strongly 

 reminds us of the production of galls in the 

 vegetable kingdom. In no case were more than 

 a single individual found tenanting the infested 

 branch.' 



It is not alone, however, species of Coryne 

 or of Syncoryne which are thus subject to the 

 attacks of a parasitical pychnogonidan. Gegen- 

 baur, as we have just said (see note to preceding 

 paragraph) has noticed it in Eudendrium ramo- 

 sum, while Ilydfaclima eckinata may occasionally 



' The occurrence of this remarkable form of 

 parasitism, which presents the unusual feature 

 of the parasite belonging to a higher group 

 than the animal infested, was first noticed by 

 me, in 185/, at the meeting of the British Associa- 

 tion for the Advancement of Science, held in that 

 year. 



A similar case has since been described, in 

 considerable detail, by Mr. Hodge, who has found 

 Syncoryne eximia infested in this way, and has re- 

 cognised in the parasite the Phoxichilidhim coccineum 

 (see ' Ann. Nat. Hist.,' 3rd ser. vol. ix, p. 33, pi. iv 

 and v). 



The first, however, to notice the liability of a 

 hydroid to become the abode of a parasitical 

 pychnogonidan was Gegenbaur, who observed 

 the hydranth.s of Eudendrium ramosum fre- 

 quently changed in form, by becoming greatly 

 enlarged, and by the reduction of their tentacles 

 to short tubercles. Here the transformed hydranth 

 was found to be tenanted by a brood of deve- 

 loping pychnogonidans (see Gegenbaur, ' Genera- 

 tionswechsel,' p. 38, note). 



A portion of a colony of Syncortfne eximia infested by 

 Phoxichilidium coccineum. 



a, A lumulusof the hydroid transformed into a sac by the 

 presence of the parasite, which has liere reached the stage at 

 which it is ready to escape into tlie surrounding water; A, a 

 ramulus, with the contained parasite at a much easier 

 stage ; c, a normal hydranth of the Syncoryne, 



