ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 797 



appendage first described by Macdonald, and seems to think that it 

 will prove to be a persistent embryonic organ ; to Jourdain its im- 

 portance seems to have been singularly exaggerated. 



/3. Polyzoa. 



Polyzoa.* — Prof. E. Eay Lankester thinks that the Polyzoa are 

 probably more closely related to the Sipunculoid Gephyrean worms 

 than to any other group of the animal kingdom, but he recognizes 

 the extreme difiiculty of interpreting the facts of their ontogeny. 



The following classification is adoj)ted : 



PODAXONIA. 



Class I. Sipunculoidea. 

 „ II. Brachiopoda. 

 „ III. Polyzoa, 



Section 1. Vermiformia. — Phoronis. 



„ 2. Pterobranchia. — Rhahdopleura, CepJtalodiscus. 

 „ 3. Eupolyzoa. 

 Sub-class 1. Ectoprocta. 



Order 1. Phylactolaema. — Lophopus, Plumatella. 

 „ 2. Gymnolsema. 



Sub-order 1. Cyclostoma. — Crisia, Hornera, Tuhulipora. 

 „ 2. Ctenostoma. — Alcyonidium, Vesicularia. 



„ 3. Chilostoma. — Cellularia, Bugula, Flustra, 



Eschara, Cellepora. 

 Sub-class 2 Entop^octa. — Pedicellina, Loxosoma, Urnatella. 



The structure of Paludicella ehrenhergii is described in detail ; the 

 terms ectocyst, endocyst, and endosarc are rejected; after a short 

 account of the different groups the author passes to a consideration 

 of the genealogical relationships of the groups of Polyzoa ; this, 

 though speculative, is " absolutely needful since zoology has become a 

 science — that is to say, an investigation of causes and not merely a 

 record of unexplained investigations." Prof. Lankester thinks that 

 the solitary ancestor was relatively larger in size and more elaborately 

 organized than the majority of living Polyzoa ; the modern form 

 has developed an elaborate system of bud-production. When the 

 complete hippocrepian lophophore became specialized in the form of 

 gill-I)lume8, the ancestral line of the Pterobranchia was started ; when 

 tlio lophophore retained its form but acquired a power of being 

 telescoped into the body, the " Eupolyzoon " appeared ; this either 

 liad its antitentacular region stalk-like, and the power of telescoping 

 limited, while tho arms of the lophophore embraced the anus, 

 when wo got tho cntoproctous type ; or tho lophophore increased 

 its telescopic capacity, tho cuticle thickened, and buds appeared 

 from all parts of tho body ; from this Pro-ectoprocton two groups 

 arose ; one produced resistcnt statoblasts, became isolated, and lived 

 in fresh water ; in tho other the arms of tho lophophore dwindled, 

 the cpistome atrophied, avicularia, tentacles, &c., became developed. 



» Eiicycl. Brit., vol. iix. (1885) pp. 420-11. 



