374 CARL VOGT. 



pressed respecting the affinities of Pedicellina and Loxosoma. 

 He not only regards them as undoubtedly Bryozoa, but more 

 than this, as the prototypes of the ordinary Bri/ozoa, and holds 

 that the primitive structure has been modified in the latter by 

 their associated life and by the formation of the ccenoecial struc- 

 tures in which they are imprisoned. 



It may be assumed, he thinks, that every primitive animal 

 must have been free, a locomotive individual, and that the fixed 

 state, as well as the colonial life, are secondary conditions 

 acquired in the course of generations. If proof were needed, it 

 might be found in the fact that the young of all fixed and social 

 animals are free. Now all the known Bryozoa are fixed, and a 

 large majority of them take the form of colonies. The only 

 kinds with isolated individuals are the Pedicellina, the Loxosomas, 

 and the Urnatella, of which the latter are very imperfectly 

 known. Loxosoma evidently exhibits the most primitive con- 

 dition amongst recent Bryozoa. The Bedicellina have made an 

 advance towards true colonization by the development of a stolon, 

 producing buds. 



The assumption of the colonial condition must bring with it 

 modifications of the primitive organisation, whilst the chief 

 features of the type would remain more or less apparent. The 

 formation of ectocysts, of cells in which the polypides are con- 

 fined, the development of retractor muscles, and the change in 

 the position of the anal orifice, are, in the Author's opinion, the 

 only important characters that distinguish the ordinary colonial 

 Bryozoa from the isolated forms, the latter in their turn possess- 

 ing a distinctive character in the stem on which the body is 

 mounted.! The structure and the arrangement of the tentacles 

 around the mouth, the conformation of the digestive canal with 



' AUman regards the stalk of Pedicellina as homologous M'ith the posterior 

 part of the cell in the unstalked forms of Polyzoa. " It is simply," he says, 

 " this portion of the cell become so much constricted as to be no longer 

 capable of containing the polypide, which is in consequence pushed onwards 

 into the wider portion which now constitutes the proper cell." (' Fresh- 

 water Polyzoa,' p. 22.) We can hardly speak of a cell, with any propriety, 

 in the case of Pedicellina, in which the body-wall lies close upon the internal 

 organs, and does not constitute a sac-like dwelling, within which the 

 polypide has the power of moving freely. But the observations of Barrois 

 on the embryonic development of the Entoprocta show that AUman's view 

 is essentially correct. After the development of the Gastrula, he describes 

 a stage in which the embryo is distinctly divided into three segments. Of 

 these the middle constitutes eventually almost the whole of the skin and 

 its contained endoderm the digestive canal ; the posterior segment gradually 

 dwindles away, and at last, with its portion of endoderm, forms merely a small 

 button-like prominence at the base of the larva, which bears a few stiff setae. 

 The stem, according to Van Benedeu's observations, is formed by the 

 prolongation of this basal prominence. It should be added that Vogt has 

 not noticed a similar stage in the case of Loxosoma.-^Trunsl. 



