360 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
style. The apertures are generally someAvhat protruding, but when 
the animal is strongly contracted may not project beyond the general 
contour of the test. They have a very variable number of lobes. The 
oral tentacles are about 24 in number, of three sizes regularly arranged ; 
those of the smallest size are inserted a little nearer the aperture than 
the others. 
The branchial sac has the four rows of long stigmata characteristic 
of the genus. The number of stigmata in a row exceeds 20. Those 
near the endostyle become successively shorter as that organ is ap- 
proached. The transverse vessels separating the rows of stigmata 
bear about ten short stout papillae, separated (except next to the median 
dorsal vessel and the endostyle where the distance is greater) from 
each other by the width of two stigmata. Practically all the papillae 
bear two slender branches of varying length, one anterior and one 
posterior. The extent to which the branches are joined to those of 
papillae of other rows to form internal longitudinal vessels varies in 
different individuals and doubtless also in the same individual with its 
age. Such unions may occur over the greater part of the sac. The 
writer has observed this in specimens both from New England and 
from Bermuda. 
Some distance beyond the stoniach, which is elliptical and smooth- 
walled, there is a well marked valvular constriction of the intestine, 
beyond which the intestine is of larger capacity and only gradually 
tapers down to its former size. Between this valve and the stomach, 
there is also a fairly constant and conspicuous constriction. The 
gland surrounding the intestine has tubules which branch repeatedly 
and end in blunt but not much expanded tips. 
There is great individual variation in the number of lobes or of 
distinct glands into which the testis is divided. It lies in the loop of 
the intestine, the parts or lobes spreading out in a fan-like manner 
from the point where the common sperm duct begins. Often the 
testis is divided up into ten or more small separate j:)yriform glands, 
each borne on a branch of the common sperm duct; in other cases 
there may be only one or two such small separate divisions, the rest of 
the organ being made up of one or two larger masses only incompletely 
cleft into lobes by deep fissures extending in toward the commencement 
of the sperm duct. The ovary is also situated in the loop formed by 
the digestive canal, along the first part of the common sperm duct. 
This species is allied to the widely distributed European form P. 
