316 



EMBRYOLOGY 



the ciliation, there appear on both sides of the head, behind 

 the post oral band of cilia, the fundaments of setae, which 

 soon elongate considerably, and finally reach approximately 

 the length of the entire larva. 



It is not to be denied that this Myzostoma larva possesses 

 a very great resemblance to the larvae of Annelids, even 



though the absence of the pre- 

 oral band of cilia, which could 

 not be found by Beard, inter- 

 feres with a complete resem- 

 blance to the Trochophore. The 

 thickened apical area, the two 

 bands of cilia, the sensory hairs 

 at the anterior and posterior 

 ends, as well as the internal 

 organization of the larva are 

 quite Annelid-like. A caudal 

 appendage, covered in the same 

 way with tactile hairs and con- 

 stituting a prolongation of the 

 ventral surface, is found in the 

 larvae of Telepsavus and Opliryo- 

 trocha. In the same way the 

 provisional setre of the Myzo- 

 stoma larva, which probably 

 arise in ectodermal sacs, point 

 to the corresponding structures 

 of certain Annelid larvfe (comp., 

 for example, the drawing of 

 Mitraria, Fig. 124, p. 276). In 

 any event the similar characters in the larvEe of Myzostoma 

 and other Annelids are very many, and the further develop- 

 ment also presents other common features, e.g., the formation 

 of the parapodia and their bristle- or hook-bearing, stump- 

 like processes. 



After the larvae have moved about free at the bottom of 

 the aquarium for some seven days, they cast off the pro- 

 visional setfe and betake themselves to an Antedon, on which 

 they are found crawling about like worms, for the larval 



Fig. 150 —Larva of Myzos^toma 

 glabrum (after Beard), a, anus; 

 h, setEe; m, mouth; s, caudal ap- 

 pendage ; sp, apical plate. 



