AGTINOZOA. 91 



. Ci-ABS II.— THE ACTINOZOA. 



Ccdenterates with a digestive sou: pa/rtially free from (he lody -cavity open, 

 ing into it below and lield in place hy six or eight mesenteries radiating fr<ym 

 tlie digestim cavity and dividing the perivisceral space into chambers. Mouth 

 surrounded with a circle of tentacles, which are Iwllow, communicating di- 

 rectly with the perivisceral chambers. A slightly marked bilateral symmetry. 

 To the edges oft/ie mesenteries (usually the free ones) are attached the repro- 

 ductive glands, both male and female, or of one sex alone ; also the craspeda, 

 or mesenterial filaments, which contain a large number of lasso-cells. Body 

 either entirely fleshy, or secreting a calcareous or homy coral-stock, and 

 when the species is social connected by a canenchyme. In some forms (sea- 

 pens) the entire colony capable of limited locomotion. No well-marked 

 nervous system, but a plexus of fusiform ganglionic cells connected by nerve- 

 pyres in tlie base of Actinians. Reproduction by self division, gemmation, 

 or by ova, tlie sexes being separate or united in tlie same individual; the 

 young undergoing a morula and gastrula condition, and then becoming 

 ■fixed. 



Order 1. Zoanthai-ia. — Mesenteries and tentacles usually six or in mul- 

 tiples of six, corallum with calcareous septa. Mesenterial fila- 

 ments abundantly developed (Astrsea, Madrepora, Actinia). 



Oi-aer 2. Aleyonaria. -^Meaentenes and tentacles always eight in num- 

 ber. Coral-stock without true septa. Mesenterial fila- 

 ments not usually numerous. Corallum usually horny, and 

 the whole colony in the Pennatulacea capable of locomo- 

 tion (Alcyonium, Gorgonia, Pennatula, Renilla). 



View of the Clabsh'ication op the Actinozoa. 



Alcyonaria. 

 (Alcyonium.) 



2!oantha/ria. 

 (Actiniii.) 



AcTmozoA. 



Laboratory Work. — Verrill has preserved Actiniae completely ex- 

 panded by slowly adding a saturated solution of picric acid to a small 

 quantity of sea-water in which they had expanded. When dead they 

 " should be transferred to a pure saturated solution of the acid, and 

 allowed to remain for from one to three hours, according to size, etc. 

 They should then be placed in alcohol, which should after a day or two 

 be renewed. Thus hardened they can be cut into sections. Corals 

 can be studied by grinding or sawing sections, and, if desirable, treated 

 as in the case of the corallum of the Millepores. 



