219 



The young sea anemone develops without any metamorphosis, 

 directly into the adult condition. Lacaze-Duthiers could not 

 determine by actual sight how fecundation of the egg takes place, 

 or whether the egg passes through a morula stage or not, though 

 he infers, with every reason, that this stage, ?*. e. x the segmentation 

 of the egg contents, takes place in the ovary. The ovaries and 

 spermaries are in the Actinia? situated in the same individual : the 

 eggs are oval, while the spermatic cells are of the usual tailed 

 form. The fecundated egg in the state in which it was first seen 

 by Lacaze-Duthiers was oval, and surrounded Fig. 75. 



by a dense coat of transparent conical spinules. 

 He was soon able to detect the presence of the 

 two primitive germinal layers, the ectoderm 

 and endoderm. Fig. 75 (from Metschnikoff) 

 illustrates the relation of the embryonal layers 

 in the larva of another polype which he calls 

 " kaliphobenartige Polypen larve ; " «, primitive 

 opening into the gastro-vascular cavity; b, c, 

 ectoderm ; d, entoderm ; e, body cavity), show- Ciliated larva of a 

 ing that the walls of the digestive cavity are Polype, 

 formed by the entoderm ; and MetschnikofFs figure shows that the 

 embryo polype has a greater resemblance to the embryo starfish 

 of the same age than the acalephs. 



Two lobes next appear within the body, these subdivide into 

 four, eight and finally twelve primitive lobes. This stage is rep- 

 resented by the corresponding stage of the coral (Fig. 77, B). Not 

 until after the twelve primitive lobes are fully formed do the ten- 

 tacles begin to make their appearance. When the first twelve 

 tentacles have grown out, twenty-four more arise, and so on, until 

 with its increasing size the actinia is provided with the full number 

 peculiar to each species. The preceding remarks apply to Actinia 

 mesembryantJiemum, but Lacaze-Duthiers observed the same 

 changes in two species of Sagartia and in Bunodes gemmacea. 



Turning now to the stony corals we will give more fully the 

 sequence of events in the life of a coral builder of the Mediter- 

 ranean, the A.stm »"<Ics c«l>jruhtris, so faithfully narrated by La- 

 caze-Duthiers. Fig. 76 taken from Tenney's "Manual of Zool- 

 ogy " illustrates this coral in various stages of expansion. 



He studied this coral on the coast of Algiers, and found that 

 reproduction took place between the end of May and July, the 



