34 The American Naturalist. 
The striking parts of the nucleoluseare, I presume, described 
by Vejdovsky in Sternaspis as “ biickelchen,” but declared by” 
Giard, in his remarkable observations upon Spio, to be the result of 
fusion of certain extra nuclear “cells” with the proper nucleolus, _ 4 
The body of the ovum is full of large yolk-spheres, staining 
dark with osmic acid, and having an average diameter of per 
2 microns. Presumably the eggs pass from the body-cavity b 
the nephridia, but no observations were made upon this point. 
Since the eggs, when laid, are concealed within a tortue 
passage removed from the external water, and as all the le 
Annelids examined are females living solitary, one in each s 
there seems a need for some special means of insuring the 
ization of these eggs. In fact, some shells contain, besides 
large female, a minute individual about 4 mm. long, which it 
thought might be a male. The only one preserved and sectior 
however, does not suffice to decide this question. In its body 
cavity there are, however, numerous cells and cilia that stron 
suggest spermatozoa in process of formation; and if this be 
case, we would have here an interesting case of dimorphism, 
least of great discrepancy in size, between the two sexes. fi 
over, these small Annelids may occur in many more cases t 
actually observed, no special attention being given to their 
tection at that time. If males, living thus in the dwelling 
female, they would furnish a ready solution of the above difficu 
in regard to the fertilization of the eggs. 
. I have not succeeded in finding this commensal Annelid i 
shells inhabited by the same hermit crab upon the New En 
coast, and believe that it, like many other of our southern 
is an undescribed species, and would suggest the name com 
asdescriptive of its peculiar habits. Its chief characters wou 
‘ asfollows: 
Polydora commensaiis, sp. n. 
| - Thefemale (Figs. 2-8). Cephalic lobe usually retracted, 
ago, the body is wide. Body flatt 
ae 100 somites; length, 25 mm.; width, 1 mm.; co’ 
ee Lo ee intestine dark, blood-vessels const 
