Page:Popular Science Monthly Volume 85.djvu/234

230 also upon the affinity of the acid for certain protein substances of the cell surface.

Mr. Frank A. Potts, of Trinity Hall, Cambridge University, reports that he found at the Murray Islands a small lobster-shaped crustacean called Alpheus which lives among the arms of crinoids and usually resembles the rich brown or mottled color of its host. Upon examining some of these Alpheus, Mr. Potts noticed numerous small pink sac-like bodies attached to their legs and these sacs contain the eggs and young larvæ of a barnacle-like animal which is evidently a parasite infesting the Alpheus. In fact this degenerate barnacle grows within the tissues of the Alpheus, and losing all semblance to a crustacean, changes into a mass of root-shaped branches which at intervals send out sac-like genital organs, these being the only special organs it possesses. When the Alpheus moults, the sacs are cast off and each little larva is doubtless liberated to wander for a time as a free-swimming minute crustacean and finally to find an Alpheus and to enter its body and change into a root-like parasite, losing its eyes, legs, antennules, and all organs of special sense to grow into a mere root-like form which sends out its genital sacs upon the legs of its unfortunate host. The name of this very degenerate creature is Thylacoplethus.

Another curious animal which attracted the attention of Mr. Potts was a crab called Hapalocarcinus, the female of which settles down while still very small and immature among the branches of the Pocillopora coral. Here the breathing of the crab produces a water current and this causes the branches of the coral to thicken and finally to enclose the crab in a capsule, leaving only a small aperture far too small to permit of its escape, but large enough to admit the minute male of the species who visits the chamber at the time the female moults.

Professor David Hilt Tennent, of Bryn Mawr College, while at the Tortugas Laboratory in Florida, discovered that the hybrid larvæ of certain echini can be caused to resemble either their father or their mother in response to definite changes in the alkalinity of the seawater. The cytology of this matter has attracted much attention and discussion, and Professor Tennent went with us to the Murray Islands to continue studies of similar import and to study other hybrid crosses between echinoderms.

He caused an artificial cross to occur between a crinoid and an echinus and carried the larvæ farther than had previously been done.

Some of Professor Tennent's best studies were carried out upon Badu Island where members of the expedition enjoyed the privilege of being the guests of the Reverend F. W. Walker, the able managing director of the "Papuan Industries, Limited," which is devoted to developing arts and crafts among the natives thus to enable them to become self-supporting in the broad civilized sense of the term, and to