Febbuaet 24, 1911] 



SCIENCE 



293 



ture as almost to veil specific difference, 

 has however chosen differently. I can not 

 say that I have seen a wholly convincing 

 number of German specimens, though 

 probably I have had opportunity, by the 

 help of collectors and the collections of 

 many museums, of seeing as many as any 

 one else, and I have further had the benefit 

 of accounts given by various workers. An 

 approximate half of the German speci- 

 mens, rather more than less, are unat- 

 tached. For the remainder I have seen 

 none that is not attached to the brachiopod 

 Chonetes sarcinulatus.^ However these 

 very strange facts may be expressed in 

 accurate percentages, the palpable evidence 

 remains, that the free and independent 

 larvaB of these closely allied species of the 

 same genus of coral have in one part of 

 the world unerringly taken a brachiopod 

 shell for a pou sto, while in another per- 

 haps actually coeval sea they have not 

 chosen a brachiopod but always a gastro- 

 pod, and usually one and the same species 

 of gastropod, for their sedentary maturity. 



Neither of these species of coral embryos 

 was deprived of a choice. The sea bottom 

 of the Coblentzian and of the Hamilton 

 stages teemed with all varieties of inverte- 

 brate remains. Gastropods and brachio- 

 pods flourished alike on both. An act of 

 choice could not pertain to the degenerate 

 and fixed adult condition of growth; but 

 it is a matter of supreme interest that such 

 an apparent act, in whatever psychological 

 category it may find its place, did manifest 

 itself in the higher stage of normal in- 

 heritance, the free and independent condi- 

 tion of early life. 



I presume that in all the phenomena of 

 commensalism which the early faunas of 



^ Pleurodiotyum of like Devonic age and with 

 its Bicetes occurs both on the Bosphorus and the 

 Maeourtt River, Brazil, but we know nothing yet 

 of its habit of fixation. 



the earth have exhibited, the concurrence 

 of the worm and the coral is the commonest. 

 Yet I have not observed it in faunas earlier 

 than the Silurian, with possible reservation 

 for the Ordovician. The Cambrian faunas 

 contain the vital elements necessary for 

 such cohabitation, but have not shown any 

 indication that this habit of interdepend- 

 ence had been formed so early, even though 

 the degenerate condition of attachment had 

 been abundantly acquired then and doubt- 

 less long before^ I shall not enter into need- 

 less detail regarding other mutual associa- 

 tions of these early days, citing briefly, for 

 convenience of reference to those who are 

 interested, the cases of the corals Favosites 

 and Amplexus recorded from the Niagaran 

 of Iowa, of a worm in the bodies of the glass 

 sponges, Hydnoceras and Prisniodictya of 

 the upper Devonian, of the barnacle Paleo- 

 creusia in a colony of Favosites, from the 

 lower middle Devonian Onondaga lime- 

 stone. 



In late stages of the Ordovician there 

 are certain erinoids of the genus Glypto- 

 crinus and other long-armed inadunates 

 which when found with arms drawn 

 together hold within them a round-mouthed 

 snail shell of the genus Cyclonema. I have 

 examined a number of these a,ssociations, 

 but have seen in none of this age any evi- 

 dence of actual attachment of the shell to 

 the proct or any other part of the crinoid. 

 Evidently here the association was a loose 

 one, the snail feeding on the fecal waste of 

 the crinoid, hanging around the back door 

 like a dog at a garbage pail. It was not 

 long after the inception of this habit, how- 

 ever, that an actual fixation ensued, and 

 there are well-known cases in the faunas of 

 the Silurian of both erinoids and cystids 

 cemented by a muscular attachment over 

 the proct of the host, so firmly as to hold 

 ' At this meeting of the society Dr. C. D. Wal- 

 cott exhibited specimens of a Cambrian worm 

 commensal with medusa. 



