INVERTEBRATE ZOOLOGY. 135 



iiig through the center of each ray as far as the tip. How many rows are 

 there ? Cnt them entirely away from a small area and notice the pores in the 

 floor of the (Diibuldcriil groove, through which they are projected. These are 

 the a )nbulacral jJoi-es. Have they a definite arrangement? In another area, 

 part the rows of feet in the middle and expose a central ridge, the nervous 

 cord, which proceeds from a central ring. Follow this out to the i)oint of a 

 ray and note the pigment eye. Ah-oral side : — Notice the plates beset with 

 spines. Are there soft spaces between these plates? Notice often in these, 

 projections c?i\\e(\. papulae . very thin portions of the integnment which pro- 

 ject out between the spines, and in the living animal are very sensitive and 

 capable of sudden withdrawal. These, as well as the ambulacral feet, are 

 used in respiration, as a special resjiiratory system fails. Search with a lens 

 among the spines for minute organs, appearing like little knobs mounted on 

 exceedingly delicate stalks. These are the pediceUariae. and appear under 

 the microscope as tiny forceps, some two- and some three-tined. They are 

 used to pick grains of sand and all forms of debris from among the spines. 

 Treatment with K-O-H will resolve the skeletal structure of these. Upon 

 the disc, at one side notice a raised circular plate, the only departure from 

 the radial symmetry. It is the viadrepore plate, a porous structure through 

 which the water passes in to the ambulacral system (see below). 



Ml. Dissection. The entire ab-oral surface should be removed, cutting 

 through the edges of the rays with the scissors, and entirely around the 

 madrepore plate, leaving it with the preparation. The disc is filled with the 

 stomach, a delicate membrane, much folded and wrinkled. Five lobes may 

 be found, which pass out a short way into the rays ; above, a very small and 

 tapering intestine leads to a minute anus, cut off bj^ the removal of the disc. 

 In each ray are a pair of brownish tree-like structures, the liepatic organs, 

 each of which possesses a central duct. The two ducts in each raj* unite into 

 a median duct, which opens into the gastric diverticulum of that ray. At 

 the base of each ray are two sexual glands (very small in immature specimens) 

 the ducts from which unite in such a manner that the glands of two adjacent 

 rays open by a common orifice in the interradial angle. The most character- 

 istic system is t\\eivater v((scnlar or ambitlacral. The madrepore plate is con- 

 tinuous with a sinuous canal, the stone catud, which may be followed into a 

 circular ridge. This ridge conceals the andndacral ring, from which five 

 radial ambidacral ves.'iels proceed through the center of each ray The course 

 of this canal is also tlirough skeletal ineces, and is marked by a median ridge 

 in the floor of each ray. From this canal, very numerous lateral branches 



