ACTINOZOA. 



91 



CLASS II. THE ACTINOZOA. 



Ccelenterates with a digestive sac partially free from the body-cavity open- 

 ing into it below and held in place by six or eight mesenteries radiating from 

 the digest ice rarity and dividing the perieisceral space into chambers. Mouth 

 surrounded icith a circle of tentacles, which are hollow, communicating di' 

 redly with the pt.ririsccral chambers. A slicihtly marked bilateral symmetry. 

 To the edges of the 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 JUaments, ichich contain a large number of lasso-cells. Body 

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

 wJien the species is social connected by a cu'nencJtyme. 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- 

 fibres in the base of Actinia ns. Reproduction by self division, gemmation, 

 or by ova, the s< .res being separate or united in the same individual; Oie 

 young undergoing a morula and gastrula condition, and then becoming 

 fixed. 



Order 1. Zoantharia. Mesenteries and tejitacles usually six or in mul- 

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

 ments abundantly developed (Astraea, Madrepora, Actinia). 



Order 2. Alcyonaria. Mesenteries 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 OP THE CLASSIFICATION OF THE ACTINOZOA. 



ZoanlJiaria. 



(AothiKi.) 



I 



Alcyonaria. 

 (Alcyonium.) 



ACTINOZOA. 



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. 



