TYPES OF CONSTRUCTION IN THE ANIMAL KINGDOM. 22$ 



to the body, and the secondary axis is at right angles or 

 transverse to this. In the course of growth repetition of 

 parts is first noticed as evidence 

 of elevation of rank, and the or- 

 ganism which has no duplication, 

 or multiplication of parts, is lower in 

 the scale, because less differentiated, 

 than one in which there is multiplica- 

 tion of parts. Where there is multi- 

 plication of parts the simplest mode 

 of arrangement is around the longi- 

 tudinal axis. When each of the 

 parts about the axis is alike there is 



radiate Structure (see the tentacles, /, F IG. S3- Coral animal and its cal- 

 careous base, Asteroides caly- 



Of Fig. 53). This is the Case in the */, Lmk. Longitudinal sec- 



tion, j. cd calcareous skeletal 



coral animal, or in the starfish, and 

 the separate parts are called anti- 

 meres ; thus the tentacles of the coral, 

 or the arms of the starfish (Fig. 54), 

 are antimeres, or opposed parts. When .there is difference 



of the colony ; _/ = chambers be- 

 tween the mesenteries. (After 

 Steinmann and Doderlein.) 



FIG. 54. A typical radiate, Starfish, Asterias areniccla,. (After Agassiz.) 



among these parts, and there are series of parts opposed to 

 each other, the differentiation has progressed one step higher, 



