PANAMIC AND WEST INDIAN ECHINID FAUNA. 219 



given my views of the effects of oceanic currents on the distribution of 

 Echini. 



As regards the distribution of Echini in the Pacific, we have at the 

 present day a condition of tilings very similar to that which must have pre- 

 vailed in the Atlantic when the species of Echini living in the Crag and in 

 the Maltese beds had their representatives in the West Indies; having, as 

 has been suggested by Gregory, found their way from the Mediterranean 

 along the shores of an ancient continent. Some of the species living on the 

 west coast of Central America have a very extended geographical distribu- 

 tion in the Pacific, and yet no one claims that this great range has been 

 brought about by their migration along the shores of a continent or con- 

 tinental islands existing between Panama and the Sandwich Islands or the 

 Marquesas. 



The great equatorial current gives us a cause fully sufficient to effect 

 such a wide distribution, and j that in a comparatively short time. While 

 undoubtedly many of the species of Echini have no pelagic plutei, and are 

 so to speak viviparous, or carry their young for a considerable period, yet 

 we should remember that young Echini, even after they have assumed the 

 characters of the adult, are capable of floating and of being transported long 

 distances by currents. It is not an uncommon thing to find the young 

 of Arbacia, of Strongylocentrotus, and of Echinarachnius floating about on 

 our coasts, and they are not unfrequently caught in the surface tow-net. 

 The same holds good for many species of Starfishes and of Ophiurans, as 

 Avell as of Holothurians. In Florida I have caught in the same way the 

 young of Cidaris, of Hipponoe, of Toxopnenstes, and of many species of 

 Starfishes and Ophiurans, during the period in which they still have the 

 huge embryonic tentacles characteristic of their younger stages, when 

 the ambulacral feet are entirely out of proportion in size to the rest of 

 the test, and the young thus possess a great floating capacity when their 

 suckers are expanded. 



They retain these suckers for a considerable period of time, during which 

 they can be transported very great distances. There is no other explana- 

 tion needed to account for the identity of the littoral marine fauna of the 

 Bermudas and the West Indies. The young and embryos of the Echino- 

 derms and Polyps of the West Indies have been carried fully six hundred 

 miles northward by the Gulf Stream at a rate of from one to three miles 

 a day, and have finally settled in the Bermudas. 



