ON THE STRUCTURE OF NOCTILUCA MILIARIS 353 



Quatrefages states that these granules may be seen to ghde from 

 the centre to the circumference, and vice versa, propelled by the 

 contractions or expansions of the transparent matrix in which they 

 are imbedded ; that new fibrous processes {expansions) arise on the 

 central mass and unite, dividing and subdividing, with the neigh- 

 bouring ones — and that if the creature be irritated, the fibres and 

 fibrils become detached from the investing membrane, and are drawn 

 in towards the mouth " like threads of a very viscid liquid, which 

 retract slowly after being broken." 



All these appearances may be very readily seen ; but I am strongly 

 inclined to believe that the greater part of them are abnormal states, 

 and that in their natural and perfectly unaltered condition, the fibres 

 and fibrils are perfectly quiescent, and present nothing to be compared 

 with the protean movements of the Auiceba. In their perfectly fresh 

 and unchanged state, in fact, the fibrous network is by no means sO' 

 obvious as it usually appears, and in such specimens I have been 

 unable to convince myself that the granules undergo any change of 

 place — certainly there is no protrusion and retraction of processes 

 to be compared with that which takes place in the Rhizopoda.^ 



The oral aperture has been satisfactorily described by Krohn. 

 Supposing the animal to lie upon its oral face (the attitude it 

 commonly assumes), with its tentacle forwards — the oral aperture 

 appears as a sort of half oval, with a nearly straight edge anteriorly,, 

 and a deeply-curved outline posteriorly (fig. 4). 



The anterior edge is not quite straight, but is formed by two 

 ridges, apparently of a harder substance than the remainder of the 

 outer membrane, which run up on the two sides of the fissure, and 

 unite, forming a very obtuse angle, open anteriorly, in the base of the 

 tentacle. 



The latter is a subcylindrical filament of i-i Sooth inch diameter, 

 more or less flattened, sometimes quite flat at its free end, which is 

 rounded at the apex. It is a little broader at its base than elsewhere, 

 and consists of an external structureless membrane continuous with 

 the general investment, and of an internal substance, which is so 

 marked by transverse granular lines, as very closely to resemble a 

 primitive fibril of striped muscle. I agree with Krohn that the 

 striation is not in the external membrane, as Quatrefages states. 



From the bottom of the oral cavity a very delicate filament (fig. 3),, 

 which exhibits a rapid undulating motion, is occasionally protruded 



1 Krohn states, that he could hardly ever cause the Noctihua: to contract by mechanical 

 or chemical irritation ; but that he once saw one which repeatedly contracted before falling- 

 into the permanently wrinkled and collapsed condition, into which they so readily jDass. 



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