12 
BULLETIN OF THE BUREAU OF FISHERIES 
larger mature group were found in August and even September, but the score of 
individuals taken are in strildng contrast with the hundreds obtained in earlier months. 
Although we have distinguished four or five stages of ovary development in our 
records, it is difficult to separate these sharply or to determine how long each lasts. 
Judging from the appearance of the ripest stages that we have recognized and of the 
young, some shrimp are spawning within 2 or 3 weeks from the date on which ovary 
development is first noticed. We may say, therefore, that in Georgia in 1931 the 
larger group was spawning from the last of April to the middle of August and that 
the young entering the commercial catch in July came from the earlier spawners 
among these large shrimp. The intervening time had been spent by the young 
probably in the smaller and more brackish creeks in feeding and growing. 
Having thus established the previous history and relations of the two groups 
found in the commercial catch of July, we may profitably complete the presentation 
of all the data on breeding and spawning that we have obtained. Like Ehrenbaum 
in his work on Crago vulgaris, we must confess to serious gaps in this phase of the 
life history. 
The Penaeidae as a group are characterized by marked sexual dimorphism, 
including certain elaborate and well-marked secondary sexual characters associated 
with sperm transfer. 
In Penaeus setiferus, in contrast to the crabs, the female is much larger than the 
male. Thus, in Georgia, in June 1931, males and females of a comparable degree 
of maturity averaged 144.5 and 156.5 mm, respectively, the females thus ex- 
ceeding the males by 8.31 percent. There are other differences in general form; 
according to Alcock (1906) the rostrum of the female is proportionally larger, a per- 
sistent juvenile character. 
The most interesting differences for the question that we are now considering 
are those of the secondary sexual characters. In Penaeus the males produce sperma- 
tophores, often of considerable complexity. The inner ramus of the first pair of 
pleopods is modified, forming a structure called the petasma or andricum. By means 
of the petasma the spermatophore is presumably transferred to the female, although 
the process as far as we know has never been observed. In Penaeus setiferus the 
endopodite of the second pair of pleopods is also modified to some extent and probably 
also plays a part in the transference of the spermatophore. 
In most species the female has on the ventral surface of the thorax between the 
bases of the last pair of pereiopods a structure of plates partially enclosing a space 
into which the spermatophore is placed. This thelycum varies greatly in complexity, 
in some species ( Penaeus brasiliensis and Xiphopenaeus kroyeri ) being well formed, 
in others less developed. 
In Penaeus settferus the thelycum is vestigial in character and does not function 
as a secondary sexual organ. The spermatophore is attached, by a gluelike secretion 
of the male, to the ventral surface of the female between the bases of the third and 
fourth pereiopods. Two winglike processes on the anterior end of the attached 
spermatophore fit securely into the grooves between the third and fourth pereiopods 
and form an inverted funnel into which the "glue” flows, fastening the spermatophore 
to the female. 
The spermatophore so attached is quite easily dislodged. This may, to a certain 
extent, explain why in Penaeus setiferus spermatophore-bearing females are much 
less abundant in the catches than are similar females of Penaeus brasiliensis and 
