146 Introduction to Animal Morphology. 



mulberry-like, while cilia appear in twelve hours. 

 The larva is apple-shaped in three days, then be- 

 comes pyramidal, developing simple, calcareous rods 

 within, and ciliated "epaulettes" on the surface 

 (except in Spatangus, in which also the calcareous 

 rods are fenestrated). The water-vascular rosette is 

 developed as usual in the eight-armed larva, which 

 soon begins to break up ; its hinder end becomes 

 absorbed, and the first trace of spines and pedicelli 

 soon appear. Finally the larval skeleton is lost, and 

 the adult form assumed. 



Anochanus Sinensis is an aberrant form with 

 spines, ambulacra, and pedicellariae, but no genital 

 glands, nor pores. It has an apical sac, in which are 

 several young echinids in various stages of growth ; 

 possibly a case of metagenesis [Griibe], or a concealed 

 form of fission, or most probably a simple case of 

 vivipareity. 



They are divisible into two orders : — 



1. Tessellata. — Palaeozoic — 5-6 series of plates, some of 

 which are hexagonal, in each inter-ambulacral space ; mouth 

 central, with a masticatory apparatus ; spine-warts weak ; 

 anus dorsal ; ambulacral plates may be in more than two- 

 rows (Melonites), or two-rowed with imperforate spine-warts 

 (Palaechinus), or perforate ; possibly passage forms to the 

 Cystidae. 



2, Euechinoidea — with two sets of ambulacral and two of 

 •inter-ambulacral plates alternating with each other. This 

 order includes two sub-orders: — i. Endocyclica or Regu- 

 laria — with central, or sub-central, round or 5-10 angled 

 mouth, with five equal ambulacral fields. This includes six 

 families: — i. Cidaridae — with perforate, smooth tubercles 

 (spine-warts) ; no peristomial notches in the corona, nor per- 

 forated tubercles on the narrow ambulacral plates. The peri- 

 stomial membrane has scales and ambulacral feet. There are 



