ORGANS FOR SPERM-TRANSFER 259 
lowed by the third, in which the external openings are differen- 
tiated but the appendages of the first somite are still simple papil- 
lae, alike in both sexes, unless they be longer in the male. 
In the fourth stage, which is about 11 mm. long, the pleopods 
of the female still are simple papillae but little longer than in the 
third stage, while in the male they are long, simple spines, point- 
ing toward one another and but slightly forward, as indicated 
in fig. 10 p. 127, Andrews, Ontogeny of Annulus, Biol. Bull., 
1906. 
The ventral face of the left spine or slightly specialized first 
pleopod, of a male 11 mm. long, is seen in fig. 16, magnified 430 
in the camera sketch. This is from a larva killed July Ist, from 
late spring hatching. The organ is like a club; it is very simple, 
nearly cylindrical and very blunt. It is not jointed, although 
there is a faint groove marking off the base from what will be 
the neck and spiral. 
On the base there isaslight ridge with depressions on the median 
side of it. Internally there are two muscles from the base into the 
sternum of the abdomem ‘The distal part of the appendage is 
slightly grooved along its ventral face, thus marking off an exter- 
nal from a median mass. In cross section, fig. 17, the shell is 
not very thick and beneath it is a well formed epidermis with 
large nuclei, from which connective tissue strands traverse the 
large blood space in which blood corpuscles float. This section 
shows the groove on the lower side. The appendage is articulated 
to a slightly elevated stump on the sternum that holds one of the 
articular muscles and part of the other and ends in an elliptical 
orifice into which the base of the stylet fits. This articulation 
is so. oblique that the stylet lies down and cross-wise towards its 
fellow and is but little elevated or directed forward. 
In the male of this stage, the openings on the fifth legs are short 
slits, not a third of the width of the above simple stylet, and to 
each slit there leads a strand of nuclei that represents the efferent 
duct. 
In males of 15 to 18 mm., in the fifth stage, the stylet (fig. 18) 
is about 1 mm. long and is somewhat more specialized. The 
base is set off from the terminal part by a more pronounced fur- 
