274 
ME. Gk J. ROMANES ON THE LOCOMOTOE SYSTEM OE MENTIS IE. 
rim of nectocalyces to be as constant a feature in the anatomy of true Medusae as is the 
presence of the polypite, the tentacula, or the nutritive canals *. 
Exception. — I must here record one exception to the numberless instances in which 
excision of the margins of naked-eyed Medusae caused paralysis of the nectocalyces. 
This single exception occurred in a species called iStaurophora laciniata , a species 
which, as I shall afterwards explain, I have made the subject of an investigation that 
necessitated the removal of the margins as the first step in each experiment. I have 
therefore removed the margin from scores of individuals belonging to this species, 
and have never met with any but this one exception to the general rule. 
In this one exceptional case, after the entire margin had been removed, there were 
still three distinct centres of spontaneity remaining. One of these centres was situated 
in the muscular tissue near the periphery of the nectocalyx, and the other two in the 
substance of the greatly extended polypite that is characteristic of this animal, one 
centre being placed in each of the two opposite arms of the cross. On carefully 
excising these three points, with as small a portion of tissue adhering to them as 
possible, entire cessation of movement ensued in the nectocalyx, while the three 
severed parts persisted in their rhythmical contractions as long as I continued to 
observe them. Regarding this exception I have only to remark that it occurred in a 
somewhat aberrant form of the true Medusae, and one which, in the unusual size of 
its nectocalyx, approached that which is usual in the swimming-organs of the covered- 
eyed Medusae. It may also be observed that, looking to the type of animal life presented 
by the order, occasional exceptions of this kind might be expected to occur ; and I am 
only surprised that within my experience they have proved themselves so rare. 
§ 2. Effects of excising the entire margins of Gonocalyces f . — Turning now to the 
covered-eyed division of the Medusae, I find, in all the species I have come across, 
that excision of the margins of gonocalyces produces an effect analogous to that which 
is produced by excision of the margins of nectocalyces. There is an important 
difference, however, between the two cases, in that the paralyzing effect of the opera- 
tion on gonocalyces is neither so certain nor so complete as it is on nectocalyces. That 
is to say, although in the majority of experiments such mutilation of gonocalyces is 
followed by immediate paralysis, this is not invariably the case ; so that one cannot 
here, as with the naked-eyed Medusae, predict with any great confidence what will be 
* The following are the species of naked-eyed Medusae on which I have made the fundamental observation : — 
JSarsia tubulosa (Saks) ; S. pulchdla (Forbes) ; S. erythrops (Romanes) ; Thaumantias inconspicua (Forbes) ; 
Bougainvillia ( Hippocrene ) superciliaris (Agassiz) ; B. rjigantea (?) (Romanes); B. fruticosa (?) (Romanes); 
Staurophora laciniata (Agassiz) ; Tiaropsis diademata (Agassiz) ; T. indicans (Romanes) ; T. polydiademata 
(Romanes) ; T. oligoploccima (Romanes) ; Stom air a chium octocostatum (Sars). 
t Although not in accordance with general usage, I extend this term to denote the swimming-organ of a 
covered-eyed Medusa. I do so because those terms which are more properly applicable to this structure are by 
some authors employed indiscriminately to designate the swimming-organs both of the covered- and of the naked- 
eyed divisions. Therefore, as it is most desirable for the purposes of the present memoir to avoid any ambiguity 
in this matter, I trust I shall be excused for thus violating the accepted terminology. 
