ANNELIDA 267 



central nervous system of the larva. At the base of the 

 ciliated cells there also lies, according to Kleinenberg, a 

 ring of muscle cells, vphich, like the ciliated band itself, is 

 made use of by the larva in locomotion. In addition, various 

 other muscle strands traverse the inside of the body ; thus 

 some extend from the apical plate to the stomach, others are 

 found in the lower part of the body, and one surrounds the 

 intestine at the point where the stomach and oesophagus 

 unite (Fig. 118 B). These muscle cells have become de- 

 tached from the mesodermal bands (Hatschek). From the 

 latter also arises the so-called head kidney, the paired excre- 

 tory organ ; it is formed from a few cells situated near the 

 pole cells, which increase greatly in length and become 

 hollow. The head kidney then extends from the pole cells, 

 that is, from the vicinity of the anus, as far as the oesophagus 

 (Fig. 118 B, Jen). It consists of a ciliated canal, which 

 may branch (as, e.g., in Folygordiiis), and of one or more 

 funnel-shaped terminations (Figs. 119 nph and 120 B, kn). 

 These do not open freely into the blastocoele, but are said to 

 end blindly (Fraipont), and in this regard therefore re- 

 semble more the excretory system of the Platyhelminthes and 

 Rotatoria. The spot v/here each of the two head kidneys 

 opens to the exterior can be seen from the figures 120 A 

 and B. 



Of the ectodermal structures of the larva there should 

 still be mentioned as important, in the first place, the eye- 

 spot, consisting of an accumulation of pigment, which in the 

 larva of Eupomatus is located in a cell of the apical region, 

 but asymetrically on the right side (Fig. 118 B, oc). The 

 two ectodermal vesicles which arise symmetrically on the 

 posterior portion of the body, each from one ectoderm cell, 

 also constitute sensory organs (Hatschek). They are pro- 

 vided with fine stiff hairs, which project into their lumina ; 

 highly refractive concrements are also found inside of them. 

 Thus they are to be recognized as otolith vesicles (Fig. 118 

 B, ot). The large sac which in Fig. 11 8 B is seen lying at 

 the posterior end of the larva arises by the enlargement of an 

 ectodermal cell. This anal vesicle appears to have no im- 

 portant significance. In Eupomatus is developed another 



