PLATE V. 



The lettering is tho same in nil tho figures. 



a Acontia. 



i Mesenteric filaments. 



c Stomata in the septa. 

 c 1 Perioral stomata. 

 c • Marginal stomata. 

 cu Cuticle. 



d Glandular streaks of the mesen- 

 teric filaments. 



c Ciliated streaks of the mesenteric 

 filaments. 

 eh Ectoderm. 

 en Endoderm. 



■I Reproductive organs. 



h Septa, rh Directive septa. 



i Oral disk. 



I- Wall. 

 I Pedal disk. 

 m Muscles. 

 mm Mesodermal muscles. 

 ml Longitudinal muscles of the septa. 

 ml 1 Retractor. 

 mp Parietobasilar muscle. 

 mi Transverse muscles. 

 mr Radial muscles of the oral disk 

 and longitudinal muscles of the 

 tentacles 

 vis Circular muscle of the wall, 

 me Mesoderm. 

 n Urticating cells. 

 o Ovicells. 



All statements given as 10 magnifying powers have reference to Zeiss's system 



Oc. 1. Oc. 2. 



a 1 6 HI n 



A 55 70 F 



C 95 125 J 



A with unscrewed front lens (unscr. A) magnifies with Oc. 1 : 30 times; with Oc 



p Filamental apparatus of the ovicells. 

 p ' Process of the ovicell. 

 p' z Apical set of epithelial cells. 



r Marginal spherules. 

 rh Directive septa. 



.i (Esophagus. 

 so Openings of the oesophagus into 



the radial chambers. 

 sr (Esophageal grooves. 

 sz Lappets of the oesophagus. 



t Tentacles and the openings homolo- 

 gous with them. 

 t ' Principal tentacles. 

 t 1 Accessory tentacles. 



o Openings of the pedal disk. 



The magnifying powers amount to 



Polystomidium jxitens. 



Fig. 1. The portion of the oesophagus, contiguous to the labial margin, with the 

 openings leading into the radial chambers ; three times the natural size. 



Fig. 2. Septum with pedal disk, wall, oral disk, cesojihagus, and mesenteric filament ; 

 natural size. 



Fig. 3. Half of the animal seen from the aboral side ; natural size. 



Fig. 4. Transverse section through the oral disk, near the oral margin. C, Oc. 2. 



Fig. 5. Transverse section through a mesenteric filament in the upper part of its 

 course. C, Oc. 1. 



Fig. 6. The entire animal, seen from the oral side ; natural size. As the only 

 specimen sent for examination was greatly injured, some restoration has been necessary. 



Fig. 7. Transverse section through the oral disk, near the stomidia. C, Oc. 2. 



Fig. 8. Longitudinal section through the upper end of the wall, the circular muscle 

 running in it and a marginal spherule. Unscr. A, Oc 2. 



Fig. 9. 



Longitudinal section through the circular muscle. D, Oc. 2. 



Fig. 10. Longitudinal section through the lower end of the wall. A, Oc. 2. 

 Fig. 11. Horizontal section through the circular muscle. A, Oc. 2. 

 Fig. 12. Transverse section through a septum. Unscr. A, Oc. 2. 



