80 



EMBRYOLOGY 



ectoderm (Kowalevsky et Marion, No. 87). In it are 

 secreted the first calcareous spictdes (sclerites) (v. Koch, Nos. 

 82 and 84, Kowalevsky'). These arise as small, highly 

 refractive bodies (.«p) within the mesodermal elements, 

 w^hich resemble migratory cells, where they soon grow into 

 small needles having lateral outgrowths. The ectodermal 

 axial skeleton of the Gorgonidse arises later than these 

 mesodermal parts of the skeleton. It must be regarded as 

 a cuticular secretion of the ectoderm of the basal foot-plate 

 (v. Koch), and at its first appearance consists of a thin 

 yellowish pellicle, which may be compared to the sheath 

 of Cornularia and Clavularia. There is soon noticeable on 

 this basal plate a small prominence, which grows up into 

 a process composed of concentrically arranged corneous 

 lamellae, and extends up between the mesenterial septa of the 



Fig. 34. — Section through the body-wall of a young attached stage of Sym- 

 podiwm coralloides (after Kowalevsky et Marion), ec, ectoderm ; en, entoderm; 

 3, mesoglcea ; sp, earliest fundament of the calcareous spicules in cells of the 

 developing mesoderm. 



primary polyp. Thus the ectoderm of the foot-plate must 



be correspondingly invaginated, and thus it comes about 



that tlie axial process of the ectoskeleton contained within 



the polyp is covered by a continuous ectodermal lamella 



(the axial epithelium), from which the further development 



of this part of the skeleton takes place. In the further 



course of development, during the progressive growth in 



length, the young polyp and the axial skeleton do not take 



the same direction ; the latter thereby acquires greater 



independence, and represents the earliest fundament of the 



whole axial skeleton which lies at the foundation of the 



entire colony subsequently produced by budding (Fig. 86 B) 



(v. Koch, No. 86 i). 



'On the other hand, Stdder (Arch. f. Naturg. Jahrg., 1887) has 



