1 lg John H. Geroüld, 



are S^w— 9|i< in length, and contain a spherical nucleus of less than 

 half that size (Fig. 80b). Their size, and the presence of a relatively 

 large and active cytoplasm, distinguish them from the nuclear 

 corpuscles just described. In older larvae (thirteen days) still 

 smaller corpuscles are found, which are about half the size of tha 

 last (5/t in length), and are probably derived from them by cell« 



division. 



The ventral nerve cord and the supraoesophageal ganglion at 

 this time become separated from the overlying ectoderm (Fig. 95-98), 

 Nerve fibrils form a large part of the dorsal portion of the cord and 

 the central part of the ganglion (Fig. 98), which has in section a 

 finely punctate appearance. The oesophageal connectives also consist 

 mainly of fibrils. The pair of hollow, hemispherical eye spots lie 

 embedded on each side of the supraoesophageal ganglion, with 

 their cavities directed laterad (Fig. 90). They consist of yellowish- 

 red, or garnet-colored, spherules. The optic nerve enters the eye 



from behind. 



Epidermal Organs. Oval clusters of ectoderm cells (Fig. 78, 99), 

 the nucleated deeper ends of which project slightly into the coelom, 

 appear at irregular intervals in the body wall of the larva of sixty 

 or seventy hours. The cuticula above some of them is elevated 

 into a slight papilla. The papillae are found at this stage in any 

 part of the body, though they appear to be slightly more abundant 

 at the extremities. These cell clusters evidently become the sensory 

 and glandular epidermal organs of the adult. They undergo only 

 slight changes, except as regards numbers and distribution, during 

 the first month of larval development (Fig. 56—57, 78). 



Nephridia. No head kidneys, like those of Polygordius and 

 the Chaetopods, are found in the trochophore of Phascolosoma. I liave 

 never found the rudiments of any nephridia whatever in this stage. 

 Even the most favorable sections of the trochophore, like the series 

 from which Fig. 82—84 were taken, afford no evidence of the presence 

 of nephridia. 



The single pair of definitive nephridia of the trunk are distin- 

 guishable in fact only after the metamorphosis has been completed. 

 There are in the early stages of their development no conspicuous 

 yellow granules, such as are found in the nephridial cells of Sipunculus, 

 and the coelom, usually from the beginning, is packed with granules 

 of yolk, so that it is difficult in Phascolosoma to trace the nephridia 

 back to their very beginning. 



