PLATE IV. 



The lettering is the same in all the figures. 



a Acontia. 



b Mesenteric filaments. 



c Stomata in the septa. 

 c l Perioral stomata. 

 c ' Marginal stomata. 

 cu Cuticle. 



d Glandular streaks of the mesen- 

 teric filaments. 



t Ciliated streaks of the mesenteric 

 filaments. 

 ek Ectoderm. 

 en Endoderm. 



g Reproductive organs. 



h Septa, rh Directive septa. 



i Oral disk. 



k Wall. 

 I Pedal disk. 

 m Muscles. 

 mm Mesodermal muscles. 

 ml Longitudinal muscles of the septa. 

 ml 1 Retractor. 

 mp Parietobasilar muscle. 

 mt Transverse muscles. 

 inr Radial muscles of the oral disk 

 and longitudinal muscles of the 

 tentacles 

 ms Circular muscle of the wall. 

 me Mesoderm. 

 n Urticating cells. 

 o Ovicells. 



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



Oc. 1. Oe. 2. 



a 1 6 10 D 



A 55 70 F 



C 95 125 J 



p Filamental apparatus of the ovirells. 

 p ' Process of the ovicell. 

 p 2 Apical set of epithelial cells. 



r Marginal spherules. 

 rh Directive septa. 



s (Esophagus. 

 so Openings of the oesophagus into 



the radial chambers. 

 sr Oesophageal grooves. 

 sz Lappets of the oesophagus. 



t Tentacles and the openings homolo- 

 gous with them. 

 t 1 Principal tentacles. 

 t - Accessory tentacles. 



v Openings of the pedal disk. 



The magnifying powers amount to 



Oc. 1. Oc. 2. 



,.. 195 240 



.. 410 550 



... 470 bid 



A with unscrewed front lens (unscr. A) magnifies with Oc. 1 : 30 times; with Oc. 2 : 40 times. 



Sicyonis crassa. 



Fig. 1. Transverse section through the upper end of the wall and the circular muscle 

 situated there. Ten times the natural size, but drawn with unscr. A, Oc. 2. On the 

 right hand side of the figure for ek read en. 



Fig. 2. A sector of the pedal disk ; natural size. 



Fig. 3. Longitudinal section through the wall of a wart-like tentacle. Unscr. A, 

 Oc. 2. 



Fie. 4. The entire animal, seen from the oral side ; natural size. 



Fig. 5. Transverse section through the basal portion of a tentacle ; about six times 

 the natural size. 



Fig. 6. Part of a transverse section through the radial muscles of the oral disk. 

 D, Oc. 2. 



Fig. 7. Part of a transverse section through the circular muscle ; enlarged more than 

 the preceding. D, Oc. 2. 



Fig. 8. Transverse section through the oral disk, and insertion of a septum. 

 Unscr. A, Oc. 2. 



Fig. 9. Septum ; natural size. 



