Cll INTRODUCTION. 



and also to two minor and intermediate modifications, 

 the one represented by Alcyonidium, :m<l tlu- other by the 

 Vesicularians. This scheme of the larval relationships of 

 the Polyzoa must, however, be regarded as purely provi- 

 sional. Notwithstanding the admirable investigations of 

 Barrois and others, we can only regard our knowledge of 

 the embryology of the Class as being quite in its infancy ; 

 and though we may probably accept as conclusive the 

 demonstration of the one primitive type, we must have a 

 much larger acquaintance with the varieties of the larval 

 form before we can safely proceed to trace the genealogy 

 and map out the courses of development*. 



GEMMATION. 



The second mode in which reproduction takes place 

 amongst the Polyzoa is by gemmation. Almost invariably 

 the budding is continuous, resulting in the formation of a 

 composite structure; in the single case of Loxosoma the 

 gemmae detach themselves from the parent, and are deve- 

 loped into solitary animals. 



The formation of the bud is a subject of the highest 

 interest ; but it is one that can only be treated satisfac- 

 torily at length, and with the help of many illustrative 

 figures. In this general sketch of the class, which is 

 merely introductory to the systematic portions of the 

 work, it would be impossible to do justice to it; and I 

 must content myself with referring the reader to some of 

 the best sources of information f. 



* On the question of the histolysis of the larva after fixation, see Nitsche, 

 Zeitsch. f. wissensch. Zool. xxi. 4 Heft, p. 59, note. 



Metschnikoffmustbe ranked as one of the first to dissent from Schneider's 

 doctrine as to the complete dissolution of the Cyphonautes-\&r\& (Nachr. d. 

 Univ. Gottingen, 1869, no. 12). 



t Van Beneden, ' Recherches,' &c., Mean. Ac-ad. B. Relg. : Allmun, 'Fresh- 

 water Polyzoa,' pp. 35-37: Smitt, CEfv. kongl. Vet.-Ak. FSrh. 186.'), n<>. \, 



