PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 99 
tions such experiments are made. What Johnston says might be ap- 
plied with equal truth to some of the acephalous mollusca, like Mya 
arenaria, for instance, which though sedentary still possesses a certain 
degree of mobility, but nevertheless is so sluggish that one may wait 
and watch for some time without detecting any evidence of activity or 
voluntary motion. The protection or security of these Jow forms is 
through the secretive faculty; the more active hiding in the mud under 
stones or upon something which is the same color as themselves, or upon 
or amid objects of brighter colors by which their own is rendered obscure 
by contrast, or else seeking security by remaining motionless. It is not 
improbable that such animals may have periods or seasons of activity, 
and perhaps in their young or adolescent stages are much freer, else the 
geographical distribution of the species would be wholly mechanical 
exterior to and independent of the organism, and like many low aquatic 
forms be dependent upon currents and upon attachment to drifting ob- 
jects, or to other and more mobile forms of animals. The activity of cer- 
tain Pectens would hardly be presupposed by the closet student through 
the form and implied ordinary habits of these mollusks, nor from any 
analogies perceptible after a study of either the structure or habits of 
such species or groups as most closely approximate to the fanshells; 
yet these footless mollusks sometimes exhibit remarkable powers of 
locomotion, equaling in performance the more active cockle-shells (Car- 
dium), which are provided with a powerful muscular foot, in its way a 
pertect leaping-pole. 
The gigantic virgularian described by me in the proceedings of the 
Cal. Acad., in August, 1873 (Verrillia Blakei*), “the fishermen say 
swims free and is so caught in their nets.”t Mr. Chambers, who sent 
a specimen of this form to the British Museum, says:{ ‘They move about 
rapidly in the water, and when brought to the surface move for a fiw 
seconds like a snake, then make a dart swiftas lightning, and disappear.” 
Dr. J. BE. Gray, from whose paper the above is quoted, also says: ‘Mr. 
Clifton describes the Australian species as swimming rapidly in shal- 
low water,” and adds: ‘“‘There seems to be no doubt that the Sea-Pens 
and Sea-Rushes do live in groups together, erect, and sunk in the mud, 
and that they are sometimes found swimming free in the sea; but the 
question is, are the free specimens those that have been disturbed by 
the waves and currents, and do they afterwards affix themselves in the 
mud, or are they vagrant specimens that live for a time and then die, 
or are eaten by fish, their struggling being mistaken for swimming?” 
Various persons referring to Verrillia have reported it as swimming 
free among the dog-fish, &c. 
A related form, probably one of those described by the late Dr. Gabb 
* Verrillia Blakei, now Halipteris Blakei. 
tDr. E. L. Moss, in Proc. Zool. Soc., London, 1873, p. 732. 
tNature, Noy. 6, 1873, p. 13. 
