103 

 Encope micropora Agass. 



['\. XIV, Fig. 7. 



On the sandy shore of the Httle island Taboguilla in the Gulf of Panama 

 this Clypeaslroid was found in considerable numbers, living buried in the 

 sand in shallow water, about low-water mark. II was found lo be ripe, 

 and ferlilizalion was undertaken on January 7th 1916. Owing to the 

 exceedingly strong development of the calcareous substance in this spe- 

 cies, the gonads being so to say infiltrated in the calcareous mass it was 

 impossible to take out pieces of the gonads as usually done by artificial 

 fertilization in Echinoderms; it had to be done in this way that the speci- 

 mens were broken to pieces and laid in water, male and female together. 

 The sexual products were thus emptied and fertilization took place. By 

 this procedure, however, the water became nearly black from the inten- 

 sive black coloration of the sea-urchin, and it was necessary to decanter 

 oil the water many times, before the culture was in good order. 



The eggs are surrounded by a thick, somewhat irregular mucilaginous 

 coat without pigment spots. The first developmental processes went on 

 very rapidly, so that already after twelwe hours the embryos had begun 

 to assume the Pluteus-shape and the skeleton had begun to form. At 

 the age of four days the posterodorsal arms had appeared, and in the 

 course of two weeks the larva had reached its full shape. The metamor- 

 phosis was not accomplished by any of the — rather few — larvae sur- 

 viving thus far. 



The shape of the larva (PI. XIV, Fig. 7) is that typical of Clypeastroid 

 larvae, presenting no specially noteworthy features. A small downward 

 curve of the ciliated band at the base of the postoral and posterodorsal 

 arms represents ventral and dorsal ciliated lobes, and a similar curve 

 between these arms on the side of the body the posterolateral lobes, but 

 all of them are small and inconspicuous. The arms are narrow, of the 

 same width throughout. There is no pigment spot in the point of the arms. 



The skeleton (Fig. 41) also shows the typical Clypeaslroid structure, 

 the body rod and recurrent rod developing in the posterior end of the 

 body into a complicated fenestrated plate, strongly thorny along the 

 posterior edge. There is both an upper and a lower ventral transverse 

 rod, the former being entirely smooth, the latter very thorny along its 

 posterior edge; the same holds good for the dorsal transverse rod. Postoral 

 and posterodorsal rods fenestrated, the latter having distinctly smaller 

 holes than the former; in both of them the holes are somewiiat larger 

 at the base, gradually diminishing in size upwards, but then remaining 

 of the same size till the end; both rods are strongly thorny, the postero- 

 dorsal rod, however, mainly along the outer side. It appears that there 



