1 62 NEW YORK STATE MUSEUM 



are of specimens so broken as to expose the ^interior. Solid flint 

 has replaced the outer part of the sponge body, but in the dis- 

 integrated silica of the interior the tube of the cloaca stands verti- 

 cal with hardened walls about which the worm tube seems to coil 

 like a beanstalk on a pole. The transparent section which is re- 

 produced from a direct print, shows with probably more accuracy 

 the actual distance of the tube from the cloaca. It is extremely 

 instructive to note that the direction of coiling is unlike in the 

 two specimens exposing the spiral, while in the section it would be 

 impossible to determine whether the course of the coiling is dex- 

 tral or sinistral. 



Barnacles and Corals 



The barnacles of today express to us one of the extreme results 

 of modification through adaptation to a parasitic condition. I 

 have ventured to suggest on a previous occasion that the Siluric 

 barnacles of the genus Lepidocoleus [pi. 5, fig. 3] are an expression 

 of these creatures before such modifications set in. It is regularly 

 segmented throughout its length, its biserial row of plates being 

 open on one side onty for the protrusion of the appendages. The 

 forms known as Turrilepas, Plumulites and Strobilepis of the 

 Devonic, are not of greatly different structure. We know hovv-ever 

 of fully modified acorn barnacles in the Devonic Protobalanus and 

 Palaeocreusia. The latter is parasitic on a Favosite coral of the 

 Onondaga limestone (Lower Devonic), in which it appears to be 

 embedded by the overgrowth of the polypites rather than b}- 

 burrowing its way into the colony as do sometimes the acorn 

 barnacles of the present [pi. 5, fig. 4, 5]. 



Crinoids and Cystids with Gastropods 



We are here presented with what appear to be instances of 

 genuinely dependent parasitism — where an attached organism 

 relies upon its host for its nutriment and existence. They con- 

 stitute the earliest instances we can cite of a dependence between 

 organisms that has become essential rather than merely convenient 

 and it is of extraordinary interest because we find some clue here 

 to the origin of the habit. The attachment of the limpetlike 

 gastropod Platyceras to the calyx of the crinoid of the Paleozoic has 

 already been referred to and many instances of it have been cited 



