380 DR F. A. BATHER. 



to satisfy. Is it not, then, simpler to suppose that the ancestors of Dendrocystis 

 possessed no exothecal subvective skeleton, and that the single appendage was developed 

 when the race had already begun the Dendrocystid mode of life ? In some of the 

 Ordovician Amphoridea [Deutocystis, Pirocystis) the intake appears at the end of a 

 short tubular extension of the theca ; but, if the animals obtained their food in the 

 usual pelmatozoan manner, we must imagine some sort of extension from this to form 

 a collecting surface, Haeckel (1896) therefore supposes the subvective system to 

 have been supported on uncalcified exothecal processes. Whether the appendage of 

 Dendrocystis arose by calcification of these, or by their absorption within a gradual 

 outgrowth from the theca, is not easy to be decided. 



§ 73. The Vent. — Thanks to the Girvan material, the position of this need no 

 longer rest in doubt. In D. scotica a number of small elongate plates, clearly grouped 

 round an opening closed by a sphincter muscle, are to be detected, not far from the 

 stem, at the edge of the lobe on the adbrachial side of the theca (§ 141 ; PL II. 

 figs. 23-25), 



§ 74. Armed with this information we may restudy Barrande's drawings. His 

 plate 26, f. 6, represents an imprint of D. Sedgwicki from Zahorzan, and a squeeze 

 taken therefrom shows the structures in their true position (PI. I. fig. 5). Three 

 features merit attention : (1) on the adbrachial side of the theca (the right-hand in 

 Barrande's figure, left-hand in ours) a definite angle, clearly outlined ; (2) between 

 this and the stem a large smooth plate, of somewhat sugar-loaf shape, with a convexly 

 curved base ; (3) a series of small plates abutting on this curved base, with some 

 appearance of regularity, and notably smaller and more elongate on the side of it 

 nearer the stem. Some or all of these appearances are also to be noticed, in the same 

 relative arrangement, in Barrande's figures 1, 14, and 16 of pi. 26, and fig. 6 of pi. 27, 

 all of which represent specimens from Zahorzan. Fig. 17 of pi. 27 is said to represent 

 the base of a specimen from d3 of Trubin, but Dr Pekner tells me that it is " surely from 

 Zahorzan d4." On its left side is the half of two concentric circles of convergent plates. 

 A very similar appearance, as seen from the side, with the sugar-loaf plate, is shown in 

 the only specimen known from d3 of Trubin, and the regularity of the appearance is not 

 greatly exaggerated in pi. 27, f. 18. It is strange that Barrande should have remarked 

 on these appearances only in order to dismiss them as unimportant. Thus, the specimen 

 mentioned last is " peu instructif " ; the concentric arrangement in fig. 17 is " due a 

 I'imagination du dessinateur" ; and in fig. 6 of the same plate " les apparences . , , 

 ont et6 exag(irees par le dessinateur," There can, however, be no doubt as to the 

 objectivity of the appearances, and the fault of the draughtsman Humbert was that he 

 seized a significance which did not commend itself to the intelligence of Barrande, 

 Haeckel, then, may have been right in regarding these concentric plates as surrounding 

 a vent, and, if the sugar-loaf plate was not precisely such a valve as he supposed, it 

 may quite possibly have served to deflect the outgoing stream in the direction of 

 the stem. 



