214 THE ANATOMY OF INVERTEBRATED ANIMALS. 



narrow bands, which surround the body. A very common 

 arrangement is one in which a band of cilia encircles the body 

 immediately in front of the mouth, the region in front of the 

 band bearing eyes, and becoming the praestomium of the adult 

 (e. g., Polyn'Oe). In such embryos, there is very commonly a 

 second band of cilia around the anal end of the embryo, and 

 a tuft of cilia is attached to the centre of the praestomium. 

 These larva? are called Telotrocha. In other cases, one or 

 many bands of cilia surround the middle of the body, between 

 the mouth and the hinder extremity. These are Mesotrocha. 



In the telotrochous larva of Phyllodoce, a shield-shaped, 

 mantle-like elevation of the integument covers the dorsal 

 region of the body behind the prae-oral ciliated ring. In the 

 larvae of the Serpulidoe, a process of the integument grows 

 out behind the mouth, and surrounds the anterior part of the 

 body of the larva like a turned-back collar. It persists, as a 

 kind of hood, in the adult. 



Some larvae are provided with setae of a different charac- 

 ter from those which are possessed by the adult, and which 

 are cast off as development advances. 



Many Polychceta multiply by a process of zooid develop- 

 ment, which, in some cases, appears to be a combination of 

 fission with gemmation ; in others, to approach very nearly 

 to pure fission or pure gemmation. The result is, not infre- 

 quently, the formation of long chains of connected zooids. 



The method of multiplication which De Quatrefages ob- 

 served in Syllls prolifera, is nearly simple fission, the animal 

 dividing near its middle, and the posterior division acquiring 

 a new head. 



In Myrianida, Milne-Edwards has described the occur- 

 rence of a sort of continuous budding between the ultimate 

 and penultimate segments, in which region new segments are 

 formed until the zooid has attained its full length. 



Frey and Leuckart and Krohn have shown that Autolytus 

 prolifer multiplies in a somewhat similar manner ; but, in- 

 stead of each new zooid being formed at the expense of an 

 entire somite, it is developed from only a portion of one. 

 Finally, I found in Protula Dysteri that, when the Protula 

 had attained a certain length, all the somites behind the six- 

 teenth became eventually separated as a new zooid ; but the 

 development of the latter is not mere fission, inasmuch as one 

 of the earliest steps in the process is the enlargement of the 

 seventeenth somite, and its conversion into the head and 



