P L Y Z A 



POLYZOA is the name applied by J. Vaughan Thompson 

 in!730 (I) 1 to a group of minute polyp-like organisms 

 which were subsequently (1834) termed "Bryozoa" by 

 Ehrenberg (2). The forms included in this group were 

 stated by Thompson to be "in a general way the whole 

 of the Flustraceas, in many of which I have clearly ascer- 

 tained the animals to be Polyzoae," they having been pre- 

 viously considered by zoologists to be allied to the Hydra- 

 like polyps. These organisms had previously been known 

 by the hard corneous " cells " or chambers which are formed 

 by the animals on the surface of their bodies, and build up, 



in consequence of the formation of dense colonies by bud- 

 ding, complex aggregates known as "sea mats" and "sea 

 mosses." Thompson expressly stated the opinion that the 

 organization of the animals detected by him led to the 

 conclusion that "they must be considered as a new type of 

 the Mollusca Acephala." 



Subsequently (1844) Henri Milne-Edwards (3) pointed 

 out the relationship of Thompson's Polyzoa to the Brachio- 

 poda, and, adopting the latter's view as to their Molluscan 

 affinities, proposed to unite these two classes with the 

 Tunicata in a group to be called " Molluscoidea." Recent 



FIG. IA. Forms connecting the Eupolyzoa and the Grphyrxa. 



1. Phormis auitralit, Harwell. 



2. One of the two nephridia of the same; ext, external aperture ; int, in?, the two internal funnel-like apertures. 



3. View of the tentacular area of Phoronis australis the tentacles cut to their bases, ft, outer line of tentacles ; it, inner line of tentacles ; m, mouth ; 



ep, epistome ; x, gap in the inner series of tentacles ; nepft, nephridio-pores ; an, anus ; gl, glandular pit. 

 (After Benham, Quart. Journ. ilicr. Sri., vol. 30, 1889.) 



4. Oolftngia urintnshii, Lankcster. Specimen in which the introvert is telescoped into the body, a, the sclerorliynchus, which with b, the scleropyge, 



represents the hard zncecium of Eupolyzoa ; c, anus. 



5. View of the same in an expanded condition, a, sclerorhynchus ; 6, scleropyge ; d, the soft introvert carrying mouth, surrounded by six pinnate tentacles. 



(After Lankcster, Trans. Linn. /Soc., 2nd ser., "Zoology," vol. ii., IHH.X) 



G. Aspi'li'siphon >Sf< enstmpii, Diesing. a, anterior corneous plate ; b, terminal posterior plate ; d, introvert. 

 (After Selenka, Die Sipunculidm, 1S83.) 



researches have entirely separated the Tunicata from this 

 association, and have demonstrated that they belong to 

 the great phylum of Vertebrata. On the other hand, the 

 association of the Polyzoa with the Brachiopoda appears 

 at present to be confirmed, though the relationship of 

 these two classes to the Mollusca has been shown to rest 



1 These numbers refer to the bibliography which will be found in 

 page 171. 



on mistaken identification of parts; see, however, Harmer 

 (18). 



The Polyzoa appear to be related to the Sipunculoid 

 Gephyrsean worms (Gephyraea inermia) more nearly than 

 to any other class of the animal kingdom. The study and 

 interpretation of the facts of their ontogeny (growth from 

 the egg) presents such extreme difficulty that in the pre- 

 sent state of our knowledge it is necessary to regard them 



