ANATOMY OF AEENICOLA ASSFMILIS. 767 



the teeth are not confined to the region immediately behind 

 the rostrum, as on cai'efid focussing they may be found also on 

 the sides of the rostrum. There is really, therefore, a circular 

 series of teeth from the centre of which the rostrum projects, 

 and the subrostral process is the lowest of this series. 

 Fig. 10 a shows the appearance of the crotchet when the 

 rostrum is in sharp focus; in fig. 10b the other teeth seen on 

 focussing slightly upwards are added. 



Each of the posterior tail segments is divided by slight 

 constrictions so as to present a tri-annulate appearance. The 

 anal segment is somewhat swollen, and the lips of the anus 

 are crenate. 



There are no gills present in any of the specimens. The 

 blood is light red in colour (in formalin). 



After staining and clearing the specimens tlie alimentary 

 canal could be well seen (fig. 18). The muscular pharynx 

 leads into the thick-walled oesophagus, which bears on the 

 dorsal surface of its posterior portion the cesophageal glands, 

 of which there are from six to eight visible on each side ; the 

 auterior one is the largest. Jnst behind this point the 

 oesophagus is slightly constricted, and the two hearts lie on 

 its lateral walls. The stomach is a wider tube, and upon its 

 walls may be clearly seen the vessels of the gastric plexus 

 bounding the chlorogogenous areas. The intestine, like that 

 of the adult, is thrown into concertina-like folds. 



Sections show that the anterior part of the oesophagus is 

 ciliated, and that the stomach is lined by columnar cells, 

 many of which contain a vacuole near the end which adjoins 

 the digestive cavity. 



In sections of the anterior ends of the two smaller speci- 

 mens the otocysts are not easily found ; they are much less 

 clearly differentiated at this stage than those of corresponding 

 post-larval stages of A. marina and A. ecaudata. Tiiey 

 are seen to be two small pits in the epidermis, the lips of 

 which are approximated so as to form a very short tube 

 (fig. 21). Each otocyst is somewhat triangular in section; 

 its apex is directed laterally and leads to the external open- 



