50 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
of cell multiplication and cell growth may, when sufficiently under¬ 
stood, give us a clue to this obscure matter of sex differentiation. From 
my observations I am led to believe that the male elements develop 
earlier than do the female elements, and further that this precocious¬ 
ness leads later to an arrested development as shown not only by the 
inferior size of the adult male, but also in the inferior development, 
so far as size is concerned, of the male germ. 
Sexual maturity in the male not only extends over a greater period 
of time than in the female but is also attained earlier. Mature sperma¬ 
tozoa were found in the chrysalis on April 12, at least one month 
before the last moult. I have found no mature spermatozoa before 
the fifteenth of February. It is perhaps safe to say that the male is 
sexually mature at about the middle of its pupation period. 
The Testis. 
In the larva the right and left testes (pi. 12, fig. 6) are separated. 
They lie in the fifth and sixth abdominal segments, between the heart 
on the dorsal side and the alimentary canal. 
The vas deferens (pi. 12, fig. 7, v. cl.) is a bent tube connected with 
the copulatory organ on the postero-ventral side, and passing thence 
upward and forward, increasing considerably in diameter to form a 
spacious receptaculum seminis. In the adult this is usually filled 
with spermatozoa either separate or in bundles (pi. 14, fig. 55). 
The vas deferens is lined with a columnar epithelium of large cells 
having very large oval or slightly irregular nuclei very rich in chroma¬ 
tin. This epithelium forms five longitudinal folds or elevations which 
are very prominent throughout its entire length. It seems clear that 
the vas deferens is homologous to the duct of a racemose gland, but 
the epithelial cells lining it evidently have a secretory function. Origin¬ 
ally this duct divides, I believe, into four branches. In Grapta silenus 
this division is very evident (pi. 12, fig. 8b). In Papilio, the division 
is not so marked (pi. 12, fig. 5, v. d.). But in both it is continued by 
four short tubes, the follicles. 
The follicles of each testis are separated by a single layer of cells 
in the form of a rather thick membrane provided with large oval nuclei. 
This same layer surrounds the follicles peripleurally, and thus binds 
the four follicles into a single organ containing four chambers (pi. 12, 
fig. 8). 
