ACTINIAN BUNODEOPSIS GLOBULIFERA. 303 



mature position at right angles with the surface, they are nearly straight. In macera- 

 tions the nematocysts appear as represented in fig. 8 b. They possess a thickened Avail, 

 and exhibit a tubu.lar appearance within, representing the tliickened basal part of the 

 thread, but no trace of the finer portion of the thread can, as a rule, be made out. 



The musculature and nerve-layer (fig. 5, nr.l.) on both sides of the mesogloea are 

 extremely delicate in the evaginations, but can be clearly recognized in favourable 

 sections. The endoderni is broader than that of the column-wall generally, and is more 

 strongly ciliated. Its cells are usually crowded with Zooxanthellce {zoox.), though in some 

 cases the alga? are very sparse or altogether wanting. The histological character, as a 

 whole, would indicate that the columnar evaginations are to be regarded as special 

 nematocyst-beariug organs. 



The size, character, and distribution of the nematocysts possess a certain importance 

 in systematic studies of the Anthozoa, and may be fittingly referred to here as repre- 

 sented throughout the different tissues of the present species. 



Carlgren (l!)0(), p. 3) believes that the nematocysts may be made of great assistance in 

 the identification of species of Actinia^ and even in the recognition of genera. For the 

 time being he roughly divides them into " thin-walled nematocysts," in which the internal 

 spiral thi'ead shows distinctly, and " thick-walled nematocysts," which appear quite 

 smooth. Very often the internal spu-al thread is not seen within the latter, while 

 in others it may be recognized, but not so clearly as in the thin-walled form. With 

 regard to their general distribution in the polyp, Carlgren finds the thin-walled variety 

 to occur mostly in the tentacles and disc, but in certain sj^jccies and genera in the column- 

 wall and stomodajum also. The thick-wtilled forms are found in all parts of the ectoderm 

 of the column-wall, and their length is fairly constant for the species. As a rule the 

 longest thick-walled nematocysts occur in the stomodaeum ; those in the tentacles are as 

 long or somewhat shorter ; while they are the shortest in the disc, column-wall, and base. 

 The longest nematocysts usually occur in the acrorhagi, or in any other special out- 

 growths of the column-wall which may be develoi)ed. 



Usually it is only in the living polyps that the stinging-cells can be examined in 

 their fully extruded state and their complete characteristics determined, including the 

 swollen basal part and the simple or complex evaginated thread. But certain distinc- 

 tions can be made out in macerations of preserved polyps, or even in sections. In the 

 species now under investigation the occurrence and character of the stinging-cells 

 are briefly as follows : — They are very sparingly I'epresented in the basal ectoderm by an 

 extremely small form of the thick-walled variety, measuring only '0] 2 mm. In the 

 column-wall they have been found only within the ectoderm of the evaginations. Here 

 they are all of one kind : large, thick-walled, slightly curved, and varying in length from 

 •038 mm. to '044 mm., with a diameter of about -008 mm. 



The tentacular nematocysts include the two varieties. By far the majority are thin- 

 walled with the spiral thread showing very distinctly, and are broad at one end and 

 narrow at the other (fig. 8«). They range in length from -018 mm. to "028 mm. The 

 thick-walled form is numerous, and nearly as long as in the columnar ev'aginations, theu" 



