On the Locomotor System of MedusjB. 247 



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

 the result of the operation just mentioned to be so uniform as 

 it is in that of the naked-eyed Medusa?. Nevertheless this 

 result, although varying greatly in different species and in dif- 

 ferent individuals of the same species, is, upon the whole, analo- 

 gous to that which is so remarkable in the case of the naked-eyed 

 Medusa) ; that is to say, in the majority of instances excision of the 

 margin of a gonoealyx is followed by a paralysis as immediate and 

 total as is the paralysis similarly caused in a nectocalyx ; but the 

 two cases differ in that (a) this is far from being invariably 

 the case, and {b) the paralysis of a gonoealyx, even when total for 

 a time, is nQA^om. 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 Me- ' 

 dusre : i. e. different genera of covered-eyed Medusse 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 anrita most resembles the 

 naked- eyed Medusae in the degree to which the locomotor centres 

 are aggregated in the margin of the smmming-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 fre- 

 quently sufficient to animate the entire nectocalyx. 



§ 4. In the covered-eyed Medusae 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. In- 

 deed I have no evidence to show that any part of the margin of a 

 gonoealyx, 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 lithocysts 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 con- 

 nexion, 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 covei-ed-eyed Medusae, is the 

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



