60 K. T. Günther 



Explanation of the plates 2 and 3. 



Abbreviatious. 



c.a cnidact. nem nematocyst. 



c.c ciicular canal. Ph the Phyllirhoe. 



c.ph cüidophor. r.c radial canal. 



ect ceto dorm. st stomach. 



eiid endoderm. ie tentacle. 



7nn manubnum. v veluiu. 



All drawings were made with a camera lucida. The high power drawings 

 with Zeiss' 4 mm Apo. objective and compensating oculars 4 and 8. 



Fig. 1. finestra parasiies Krohn with two tentacles fully developed, as seen 



with the aboral side of the medusa, or the ventral aspect of the 



Phyllirhoe turned towards the spectator. 



The centrai stomach, radiai canals, velum etc. are seen by trans- 



parency. 

 Fig. 2. The same individuai reft from the Phyllirhoe and viewed from ita 



orai surface. 



The aboral portions of the cnidacts are seen through the transpa- 



rency of the jelly. 



This individuai Mnestra is abnormal in that one cnidact is divided, 



and the radiai canal diametrically opposite is beut, having obvìously 



received some injury during the course of development. 

 Fig. 3. Ectoderm cells on the exumbrella of a healthy Mnestra. Prep. Kleinen- 



berg's picrosulphuric and haematoxylin. 

 Fig. 4. Ditto. Prep. Osmic acid. 

 Fig. 5. Ectoderm cells on the exumbrella of a Mnestra believed to bave been 



in bad health. 

 Fig. 6. Ectoderm as seen in a living individuai which had been living for 



6 hours in seawater tinged with soluble Carmine. 

 Fig. 7. Cnidoblasts, with nematocysts and interstitial cells from a portion of 



a cnidact. 

 Fig. 8. A portion of a cnidact with 2 — 3 rows of cnidoblasts. The nemato- 

 cysts have discharged their threads. 

 Fig. 9. Transverse section acroas such a cnidact as is figured in Fig. 8. 

 Fig. lu. Portion of exumbrella with the terminal portion of a cnidact seen 



partly in prolile. Note the elongated jirocesses which connect the 



neighbouring ectoderm cells with the cnidact. Prep. Osmic acid. 

 Fig. 11. Near the line of junction of the velum and the subumbrella are seen 



5 nematocysts, belonging to the marginai ring of cnidoblasts and the 



cpitholium of the circular canal (c.c). 

 Fig. 12. Musculature of the subumbrella. 

 Fig. 13. Muscle celi from the velum (after Claus). 



