252 ECTOPROCTA. 



is somewhat doubtful. It was regarded as muscular by Claparede 

 (No. 309), though this, as shewn by Schneider, is no doubt a 

 mistake. Allman (No. 305) regards it as hepatic, and Hatschek as a 

 thickening of the epidermis. Close to each of these organs is a 

 small body regarded by Claparede as an accessory muscle. It is 

 placed in the normal position for a Polyzoon ganglion, and may 

 perhaps be therefore regarded as nervous in nature. Allman points 

 out its similarity to a bilobed ganglion, but is not inclined to take 

 this view of it. The constitution of the parts contained in the 

 anterior cavity (x) is somewhat obscure. The most elaborate descrip- 

 tions of them are given by Schneider and Allman. Lining the 

 cavity is apparently a mass of spherical bodies, connected with which 

 is a tongue-like process provided with long cilia, which can be protruded 

 from the orifice. Internal to this is a striated body. A good figure 

 of the whole structure is given by Schneider. 



The general similarity of Cyphonautes to the other larva? is quite 

 obvious from the above description and figure. In the presence of 

 an anus, a vestibule, and possibly a nervous system, it clearly exhibits 

 a far more complicated organisation than any other Polyzoon larvae 

 except those of the Entoprocta. 



The post-embryonic metamorphosis of Cyphonautes, admirably 

 investigated by Schneider, takes place in the same manner as that 

 of other larvse, and is accompanied by the degeneration of the larval 

 organs, and the formation of a clear body, which gives rise to the 

 alimentary cavity and lophophore of the fixed polype. The larval 

 shell takes part in the formation of the ectocyst of the polype. 



Cydostomata. We owe to Barrels by far the fullest account of the 

 development of the Cyclostomata, but how far his interpretations are to 

 be trusted is very doubtful. The larvse differ very considerably from the 

 normal larvae of the Chilostomata and Ctenostomata ; the difference being 

 mainly due to the enormous development of the ciliated disc. Barrois has 

 investigated the larvse of three genera, Phalangella, Crisia, and Diastopora, 

 and states that they very closely resemble each other. The ovum is ex- 

 tremely minute. 



The segmentation, so far as it has been made out, is regular. During 

 the segmentation growth is very rapid, and eventually there is formed 

 a blastosphere many times larger than the original ovum. The blasto- 

 sphere becomes flattened, and is converted into a gastrula by bending up 

 into a cup-like form. The gastrula opening is stated to remain as the per- 

 manent mouth, which has a terminal and central position. A transverse 

 ring-like thickening is formed round the larva, which probably corresponds 

 with the ciliated ring of previous larva? ; and the body of the larva in 

 front of this ring becomes ciliated. The aboral end of the larva becomes 

 thickened, and grows out into an elongated prominence, which probably 

 corresponds to the ciliated disc. The ring before mentioned becomes 

 at the same time more prominent, and forms a cylindrical sheath for the 

 ciliated disc. At the time when the larva becomes liberated from the 

 maternal cell it has the form of a barrel with a slight constriction in 

 the middle separating the oral from the aboral end. At the centre of the 



