496 THE ANATOMY OF IXVERTEBRATED ANIMALS. 



pores on the genital plates, through which their products are 

 extruded. Hoffmann has found the peritoneal fluid of the 

 males full of spermatozoa. 



Fig. 145.— Development of an Echinid. (After Muller.)— A, Echinopscdium of Echi- 

 nus pulchellus in the gastrula stage. B, fully-developed Echinopsedium (Plutetis) 

 of the same species: a. mouth; b, stomach and intestine; c. anus; A F, processes 

 of the body into which prolongations of the internal skeleton extend. C, the 

 Echinopasdium of an Echinid in which the Echinoderm is so far advanced that 

 the spines, pedicels, and pcdicellarise are visible. D, Echinop;edium of Echinus 

 lividus: a, tnoutli; a', pullet; 6, stomach; //, intestine; c, rudimentary Echino- 

 derm; c', the ambulacra! sac; c", the external opeuing of its duct; A A, F F, B, 

 the processes of the body. 



In the Echinidca, as in the Ophiuridea, the Echinopaa- 



