166 



P L Y Z O A 



loped on the stalk of a Rhabdopleura polypide do not 

 detach themselves, we find that we can trace the stalk of 

 each polypide of a colony into connexion with the stalk of 

 the polypide from which it was originally budded, which 

 may now be considered as a " branch " bearing many- 

 stalked polypides upon its greatly extended length, and 

 such a " branch-stalk " may be further traced to its junc- 

 tion with the " stem-stalk " of the whole colony. The 

 stem-stalk was at one time the simple terminal stalk of a 

 single polypide, but by lateral budding it gave rise to 

 other polypides, and so became a gemmiferous " branch " ; 

 and further, when some of these in their turn budded and 

 became branches, it became the main " stem " of a copious 

 colony. 



A serious error has been made in comparing the contrac- 

 tile stalk of the Pterobranchiate polypide to the "funi- 

 culus " or cord-like mesentery of Eupo- 

 lyzoa. With this it has morphologi- 

 cally nothing in common, since it is 

 not an internal organ, but simply the 

 elongated termination or stalk of the 

 body, comparable to the stalk of Pedi- 

 cellina (fig. 15) and Loxosoma (fig. 16), 

 or to the hydrocaulus of such a Hydro- 

 zoon colony as Cordylophora. The 

 stalk where it bears only very young 

 buds, or none at all, as is always its 

 condition in Cephalodiscus and in many 

 polypides of a Rhabdopleura colony, 

 may be called a "gymnocaulus"; when 

 once its buds have devel- 

 oped into full grown poly- 

 pides, and it has elongated 

 proportionally with their 

 growth, it becomes a "pec- Fla . IO.-A polypide of Cephalodiscus do- 



tOCaulus"' that is tO Say it decalophus, from which the lophophore- 



is to that part of it which 

 bears such polypides that 

 this term may be conveni- 

 ently applied. The pecto- 

 caulus of Rhabdopleura, both in the form of branch and 

 stem, undergoes remarkable change of appearance as com- 

 pared with the gymnocaulus. It loses its contractility, 

 shrinks, and develops on its surface a hard, dark, horny 

 cuticle (whence its name), comparable precisely in its nature 

 to the hardened cuticle which forms the zooecia of Eupo- 

 lyzoa. It now has the appearance of a black cord or 

 rod-like body lying within and adherent to the inner face 

 of the much wider tubular stem, and branches formed by 

 the gradual building up and arborescent extension of the 

 annulated tubarium secreted by the individual polypides. 

 It has been regarded both by Allman and by Sars as a 

 special structure, and called by the former " the chitinous 

 rod" or " blastophore," by the latter "the axial cord." 



In reality it is the black-coloured pectocaulus of 

 Rhabdopleura which corresponds to the ccenoecium of an 

 ordinary Polyzoon ; whilst the term " ccenoecium " is 

 totally inapplicable morphologically to the annulated 

 branched tube in which the Rhabdopleura colony lives, 

 this having absolutely no parallel in the Eupolyzoa. 



A sac-like testis has been discovered in Rhabdopleura 

 opening by the side of the anus (Lankester, 7) ; but the 

 ova have not yet been seen, nor is anything known of its 

 development. Similarly the eggs of Cephalodiscus are 

 observed within the body of the parent in the " Chal- 

 lenger" specimens, but nothing further is known of its 

 life-history. 



A body-cavity is present (Lankester), though its exist- 

 ence has been denied by Sars and by M'lntosh. Neph- 

 ridia and nerve ganglia are not described. Cephalodkcus 



tentacles and buccal shield have been 

 removed in order to show the remark- 

 able eyes, a, buds; c, stalk; ff, eyes; 

 A, post-oral collar, hidden by the buccal 

 shield in flg. 9. (Original drawing by 

 Prof. M'Intosh F.R.S.) 



has two remarkable eye spots dorsal to the cephalic disk 

 (fig. 10, ff). 



THE EUPOLYZOA. 



Whilst it is necessary to include in the group Polyzoa 

 the forms we have already noticed as Vermiformia and 

 Pterobranchia, there can be no doubt that those organisms 

 to which we assign the name Eupolyzoa are primarily 

 those upon which naturalists have framed their concep- 

 tion of the group, and that they constitute a very con- 

 sistent assemblage, held together by well-defined characters, 

 and yet presenting an immense number of varied forms 

 showing a wide range of modifications. 



All the Eupolyzoa have closely approximated mouth 

 and anus, and, like Paludicella, a complete range of hollow 

 ciliate tentacles, describing either a circle or a horse shoe, 

 surrounding the mouth. The anus as well as the mouth 

 is included in this area in a few exceptional forms (the 

 Entoprocta) ; it lies near but outside the lophophore (as the 

 area is termed) in the vast majority (the Ectoprocta). 

 Except in the Entoprocta, where the movement is limited, 

 the whole anterior portion of the body bearing the 

 lophophore can be invaginated into the hinder part (as 

 described above for the typical Eupolyzoon Paludicella). 

 This character distinguishes the Eupolyzoa from both 

 Vermiformia and Pterobranchiarr The polypides of all the 

 Eupolyzoa are minute, but all produce buds which remain 

 in organic continuity with their parent (except in Loxo- 

 soma) and build up very considerable and sometimes 

 massive colonies. 



In all Eupolyzoa the cuticle of the hinder part of each 

 polypide is thick and dense, thus forming a hard-walled 

 sac, the zooecium. This is peculiar to and universal in 

 the Eupolyzoa (except Loxosoma), and is not to be 

 confounded with the non-adherent tubes of Phoronis and 

 Rhabdopleura or the jelly-house of Cephalodiscus. The 

 connected zocecia of a colony of Eupolyzoa constitute a 

 ccencecium. A simple nerve ganglion between mouth and 

 anus, a large body-cavity (except in Entoprocta), simple 

 gonads without accessory glands or ducts, usually testis 

 and ovary in the same polypide, absence of a blood-vascular 

 system, of any but the most rudimentary nephridia, and 

 of eyes, otocysts, or other special sense-organs, are features 

 characterizing all adult Eupolyzoa. 



The section Eupolyzoa, with its vast number of species 

 and genera, requires a somewhat elaborate classification. 

 The forms in which the anus is enclosed within the 

 tentacular circle are very few, and are peculiar in other 

 respects. We follow Nitsche (8) in separating them as 

 the sub-class Entoprocta from the majority of Eupolyzoa 

 forming the sub-class Ectoprocta. 



Sub-class 1. Ectoprocta, Nitsche. 



Eupolyzoa with the anus not included within the area 

 of the lophophore. Anterior portion of the body of the 

 normal polypide introversible. Tentacles not individually 

 capable of being coiled or flexed. 



Order 1. PHYLACTOL^MA, Allman. 



Ectoproctous Eupolyzoa in which the polypide possesses 

 a prse-oral lobe or epistome, similar to that of Phoronis, 

 and comparable to the more highly developed buccal 

 shield or disk of the Pterobranchia. Lophophore (except in 

 Fredericella, where it is nearly circular) horse-shoe-shaped 

 (hippocrepian). Polypides of a colony equi-formal, that is, 

 not differentiated in structure and function. Neighbouring 

 zocecia are in free and open communication, the bud never 

 becoming shut off by a perforated cuticular plate from its 

 parent. Cuticle of the zocecia either gelatinous or horny, 

 forming massive or else arborescent ccenoecia, in one genus 



