In now submitting the second instalment of my observations on the locomotor system of Medusæ to the consideration of this Society, I should like to preface the communication with a few words to explain why several experiments which I had intended to perform this season have been unavoidably postponed. It is well known to naturalists that, from causes which are not very well understood, the numbers of Medusæ in the same localities are subject, in different years, to considerable variations. Now on the part of the coast where my work has throughout been carried on—viz. the Cromarty Firth, on the east of Scotland—the Medusæ have been this year as scarce as last year they were abundant. Probably the cause of this scarcity in the land-locked position occupied by the Cromarty Firth is in part to be attributed to the unusual prevalence of westerly winds which has this year been observable in that locality. But whatever the cause, the fact of this scarcity having existed has compelled me this year to restrict my observations, almost exclusively, to the genera Sarsia , Tiaropsis , and Aurelia . By way of introduction it is only necessary further to state that, for the sake of facilitating reference, I shall endeavour to construct the present communication on as nearly as possible the same general plan as the last one. 1. Effects of excising the entire margins of Nectocalyces . —Under this heading I have very little to add to the statements contained in my former paper. Many of the experiments which I have this year performed have necessitated, in a vast number of instances, the removal of the extreme periphery of nectocalyces; and in no one instance have I found an occurrence of even the slightest deviation from the general rule previously enunciated—the rule, namely, that “excision of the extreme margin of a nectocalyx causes immediate, total, and permanent paralysis of the entire organ".