504 DR F. A. BATHER. 



any, their reduction to less than two is inexplicable. One concludes, therefore, that it 

 had none. On the other hand, one would expect to find its intake raised on some 

 rudimentary extension of the theca, such as might afford a starting-point for the 

 subsequent outgrowth. An extension of this kind is seen in the slightly older 

 Piracy stis and in Deutocystis, a contemporary of the Bohemian Dendrocystis. 



§ 589. Increased knowledge of the stem in Dendrocystis has not weakened my 

 conviction that this organ was evolved as an outgrowth from an irregularly plated 

 theca. The preceding stage is seen in the Cambrian Cigara (§ 87). Indications of 

 what yet earlier stages may have been are still afforded by such Ordovician genera as 

 Aristocystis and Pii^ocystis, but even more conspicuously by Pilocystites primitius 

 Barrande (1887, p. 185, pL 2, f. 26) also from the Cambrian (Paradoxidian) of 

 Ginetz (Bather, 1896, p. 297). 



Other modifications that have to be discounted in this search for a forefather are 

 the geomalic extension of the theca and the migration of the vent. 



§ 590. Thus the ancestor of Dendrocystis gradually emerges from Cambrian or 

 Precambrian darkness, with an ovoid theca of small irregular plates, stretched out 

 below for attachment to the sea-floor or some fixed object ; with the intake at the 

 other pole, raised a little above the general surface, so as to clear the adjacent vent, 

 and surrounded with uncalcified tentacles having sensory, and probably subvective, 

 functions. There were no special organs of respiration, but the anus was doubtless 

 " contrived a double debt to pay." As for hydropore and gonopore, they may yet be 

 discovered in the Heterostelea ; meanwhile we can say nothing. 



§ 591. The second representative of the Heterostelea found in Girvan, namely, 

 Cothurnocystis, shows the geomalic tendency very strongly developed ; but in this 

 case there is no accompanying tendency to bilateral symmetry or to axial growth, 

 because other forces have intervened. The argument by which the peculiar shape and 

 structure of this animal is shown to be in strict relation to its mode of life need not 

 be recapitulated (§§ 223-244). Put briefly, we may look on Cothurnocystis as a 

 Pelmatozoon that has relinquished the normal pelmatozoic habit, but instead of merely 

 modifying it, as in the case of Dendrocystis, or adopting an eleutherozoic existence, 

 has worked out for itself an original and novel kind of statozoic life. The stem may 

 or may not have been the balancer and rudder that I suppose ; at any rate, it is no 

 longer an organ of attachment. The theca is fixed, though not immovably, by its side, 

 that is to say, by the under-face of the extension-plane. The intake does not remain 

 at or near the a-columnal pole, but has moved on to the upper face of the extension- 

 plane. Thus, relatively to gravity, the attachment and the intake are precisely as m 

 a normal Pelmatozoon ; but, morphologically, they are quite different. In harmony with 

 the sanitary principle, the vent is as far removed from the intake as the structure of 

 the animal permits ; but in this case it appears to be the intake that has shifted its 

 position, while the vent has maintained the a-columnal situation which it occupied in 

 the immediate ancestors, as well as in the primitive pelmatozoic ancestor. Such a 



