144 Mr. Gr. J. Romanes on the [Dec. 16, 



§ 2. In the case of the covered-eyed Medusas I have not found the 

 result of the operation just mentioned to be so uniform as it is in the 

 case of the naked-eyed Medusas. Nevertheless this result, although 

 varyiug greatly in different species and in different individuals of the 

 same species, is, upon the whole, analogous to that which is so remark- 

 able in the case of the naked-eyed Medusas ; that is to say, in the majority 

 of instances excision of the margin of a gonocalyx is followed by a para- 

 lysis as immediate and total as is the paralysis similarly caused in a nec- 

 tocalyx ; but the two cases differ in that (a) this is far from being 

 invariably the case, and (b) the paralysis of a gonocalyx, even when total 

 for a time, is seldom permanent. After periods varying from a few 

 seconds to half an hour or more occasional contractions begin to take 

 place, or the contractions may be resumed with but little change in their 

 character and frequency. 



These remarks apply to gonocalyces in general ; but they do not apply 

 in equal degrees to all the genera of covered-eyed Medusas : i. e. different 

 genera of covered-eyed Medusas manifest, in their constituent individuals, 

 different average degrees of paralysis when subjected to the operation we 

 are considering. Of all the species I have come across, Aurelia aurita 

 most resembles the naked- eyed Medusas in the degree to which the 

 locomotor centres are aggregated in the margin of the swimming-organ ; 

 for in the case of this species it frequently happens that the paralysis 

 caused by excision of the margin is permanent. 



§ 3. In the genus Sarsia I find that excision of the eye-specks alone 

 causes a greater degree of paralysis than does excision of the intermediate 

 portions of the margin alone ; for while the former operation is usually 

 sufficient to cause temporary and sometimes permanent paralysis, the 

 latter operation never causes either. That all parts of the marginal 

 tissue between the eye-specks, however, are capable of originating impulses 

 to contraction, is proved by the fact that the smallest atom of this tissue, 

 when left in situ after all the rest of the margin has been removed, is 

 frequently sufficient to animate the entire nectocalyx. 



§ 4. In the covered-eyed Medusas I find that the concentration of the 

 marginal supply of locomotor centres into the marginal bodies is even 

 more decided than it is in the case of Sarsia. Indeed I have no evidence 

 to show that any part of the margin of a gonocalyx, other than the eight 

 lithocysts, has any function of spontaneity to perform ; so that all the 

 remarks made in § 2, while stating the effects of removing the entire margin 

 of gonocalyces, are equally applicable to the effects of removing the litho- 

 cysts alone. I may add that in the case of Aurelia aurita, which from 

 its flattened shape admits of the fairest experiments being made in this 

 connexion, all the spontaneity of the margin, and so in many cases of the 

 entire animal, is without question seated exclusively in the lithocysts *. 



* In no -case, either among the naked- or the covered-eyed Medusae, is the polypite 

 affected by removal of the periphery of the swimming-organs. 



