202 



TERATOLOGY AND PATHOLOGY. 



Tig. 7G. 



be seen to be similarly affected. In this liydroid the infested hydranths become converted into 

 laro-e oval sacs, each enclosing numerous individuals of a pychnogonidan in various stages of 

 development. The parasite appears to be here of a different species from that of the Spicorpie, 

 but I have not follovt'ed it to a sufficiently mature stage to enable me to determine it. 



The infested and transformed hydranths of llydractinia may be seen associated with other 

 perfectly normal ones in the same colony. Their transfonnation will be found in various stages 

 of completeness, some still possessing short stunted tentacles, while in others the tentacles will 

 have entirely disappeared. The parasite is here, as in the case already described, most likely 

 introduced in the state of egg by being swallowed cither by the infested hydranth or by some 

 other hydranth of the colony. 



Dr. Strethill Wright was the first to notice the liability of Ilydradinia to the parasitical 

 attack of a pychnogonidan,^ and his statements are fully borne out by ray own observations. 



The misshapen club-like branches which Van Beneden figm-es in his Eudendrium {Bouf/ain- 

 villia) ramosuni- originate most probably in a similar case of parasitism. 



Other abnormal conditions. — Besides the changes of form dependent on parasitism there are 

 others by no means destitute of morphological and physiological interest. 



While examining the medussB which had been thrown off from a colony of Spicori/ne jiiil- 



chella in one of my jars, I was struck by 

 ob.serving two of these medusae united to 

 one another by a small space on the convex 

 surface of their umbrellas, at a short dis- 

 tance from the summit (woodcut, fig. 7G). 

 One of the united medusse was a little 

 smaller than the other; but otherwise they 

 were both equally developed, and presented 

 the ordinary condition of these zooids at the 

 time of their liberation from the trophosome. 

 The cavities of the two rmibrellse freely com- 

 municated with one another through the 

 surface of junction. 



That neither of the medusa; thus so in- 

 timately united had been produced by a bud 

 from the other was evident ; for the original 

 point of union with the trophosome, as 

 well as the remains of the canal, by which 

 the cavity of the manubrium had at one 

 time communicated with the somatic cavity 

 of the trophosome, were still distinct in each, 

 while these facts are also opposed to the 

 view which would regard the twin raedusa3 as representing a single one in the process of self- 

 division. 



Conjoined tuin nu'dusa-, developed from a specimen of 

 Si/ncort/ne j>ulchella. 



' Proc. Roy. Plivsical Soc. Edinburgh,' November, 1861. 

 ' I;'Eml)ryogeiiie des Tubulaires.' 



