ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 493 



marked the further we are removed from the Entoprocta ; in con- 

 sequence of this the oral surface, which was at first entirely enclosed 

 in the interior of a cavity (the vestibule) and covered over by the 

 aboral surface, has gradually passed more and more to the exterior so 

 as to form by itself the external integument and to drive the aboral 

 surface into the interior of a cavity (the pallial cavity). In the most 

 differentiated types of the Chilostomata and Ctenostomata we have 

 seen that the aboral surface has been driven into the interior ; not- 

 withstanding this, the uppermost portion of this surface which forms 

 the organ called the " calotte " has always been seen to be projecting. 

 In the Cyclostomata, however, the pallial cavity is always closed and 

 covered over. Adding to these the Lophopoda, we may make the 

 following table : 



Ento eta ^ ( Predominance of the aboral surface. Vestibule 



P \ at its maximum. Intestine well developed. 



Chilostomata and ( Predominance of the corona. A pallial cavity. 



Ctenostomata (sac reduced) \ The intestine reduced to a mass of globules. 

 Cyclostomata and ( Predominance of the oral surface. Pallial cavity 



Lophopoda (no sac). \ at its maximum. Intestine disappeared. 



The author points out that from the point of view of larval forms 

 only we seem to find an essential character in the antagonism of the 

 two great cavities at the poles, and, when we carry this further, in the 

 greater or less development of the mantle. It is according to the ex- 

 tension of this last that we find one or other of the two surfaces of 

 the larva best developed ; when there is a median extension of the 

 mantle we find, moreover, that the intestine has partly disappeared ; 

 while when it is at its maximum condition of extension there is no 

 intestine at all. When we come to look at the matter in a more 

 general way we see that this development of the mantle is not a 

 matter of so great importance, inasmuch as every form of larva, no 

 matter to what type it belongs, can always be referred to a common 

 type, in which there is no mantle, in which the oral surface is always 

 within the vestibule, and the aboral forms an integument. The 

 history of the mantle is, then, only a history of a series of adaptive 

 modifications. 



Dealing with the mechanism of the metamorphosis, M. Barrois 

 finds that if we try to construct a general type of adult Bryozoon we 

 have to recognize (1) a foot corresponding to the oral pole, (2) the 

 frontal surface, corresponding to that which answers to the oral, and 

 (3) a tergal or anal surface. In the Entoprocta these can be easily made 

 out, but in the Ectoprocta it is not always so distinct ; in the forms 

 where the zocecium is elongated we seem to have the primitive dis- 

 position, in the flattened ones the tergal surface is increased in extent ; 

 palingenesis is to be seen in the Ectoprocta, ccenogenesis in the 

 Entoprocta, 



As the author regards the Bryozoa as belonging to the Vermes 

 he notes that, with the exception of the Botifera, the Bryozoa 

 are the only Vermes in which a telostomiate condition is con- 

 stantly manifested, either in the larval or in the adult condition ; 

 in other words, the division of the body is on the primitive or gastrula 



