sipunculidj: 363 



detached from the peritoneal epithelium, and are found 

 floating free in the body cavity. 



The metamorphosis of the Si'punculvs larva into the adult 

 animal is first indicated in the considerable growth of the 

 body and the reduction of the head portion. Connected 

 with this is the complete displacement of the mouth to the 

 anterior end and the further shoving forward of the anus, 

 the latter being brought about by the more i^apid growth of 

 the extreme posterior portion of the body. The ciliated 

 band gradually atrophies. It has nothing to do with the 

 development of the tentacles, which take their origin as 

 evaginations of the margins of the mouth. The brain arises 

 from the lower layers of the apical plate, which has become 

 several layers thick. The ventral nerve cord arises in the 

 ventral middle line from an ectodermal thickening, which 

 progresses from in front backwards. The oesophageal con- 

 nectives grow from its anterior end towards the brain, 

 therefore in a direction opposite to the growth of the ventral 

 cord, and contrary to the method of outgrowth in the Anne- 

 lida, where the apical plate grows out into the connectives. 



Two additional pigment spots are added to the two wbich 

 had already arisen in the larva in connection with the apical 

 plate (Fig. 158 F). The provisional organs of the intestine — 

 the glands and the so-called pharynx — atrophy ; the intes- 

 tine itself increases in length and is thrown into several 

 loops (Fig. 159). On the dorsal side of the intestine there 

 arises from its mesodermal covering a blood-vessel ; but this 

 does not take place until quite late. The longitudinal and 

 circular muscle-layers of the dermo-muscular sac are differ- 

 entiated much earlier. The nephridia are said to undergo 

 a peculiar change, terminating internally in vesicular en- 

 largements, while their external openings are retained. 



The condition of the nephridia recalls the statements made by Schau- 

 INSLAND that in the Priapulidae the nephridia are closed and, on the one 

 hand, function with their blind ends as excretory organs, while, on the 

 other hand, they are directly united with the germaria, and, in fact, accord- 

 ing to Schauinsland's description, even ai-ise from the latter. Thus even 

 in closed nephridia their function as an efferent apparatus of the genital 

 products would be explicable. It should be mentioned, however, that 



