186 U.S. NATIONAL MUSEUM BULLETIN 291 



vae are present in the 4-11 mm size range, but the plot for larger 

 larvae and juveniles (12-23 mm) constitutes a secondary peak in the 

 curve, vt^ith a large number of individuals in the 12-15 mm category. 

 The slight depression between 24-31 mm represents individuals in 

 the maturing stage. Most males, particularly by 28-31 mm, are ripe, 

 but females are only in the beginning of the maturing stage. The major 

 peak in the sample population is composed of individuals from 32^7 

 mm in ML; in this range all the males are ripe and the females are 

 maturing and ripe. At about 48 mm the population, composed of ripe 

 males and ripe and spent females, decreases rapidly in numbers. There- 

 fore, the portion of the sample population that occurs with the great- 

 est frequency has individuals that are near or in the spawning 

 conditions. 



Although the sex ratio of males to females in the overall population 

 is 1:1, some marked differences occur within certain size groups. In 

 general, there are a few more males than females in the juvenile and 

 maturing stages up to the 28-31 mm category. There are several more 

 males than females in the 32-39 mm group where all the males are 

 ripe and the females are maturing or ripe. A large difference occurs 

 in the 40^3 mm increment where there are 47 males and 26 females ; 

 i.e., only 36% of the specimens in this category are females. A sudden 

 reversal of the predominance of males occurs above the 40^3 mm in- 

 crement. Only a few more females than males exist in the 44-47 mm 

 class, but above that the males drop off sharply in numbers so that in 

 the 48-51 mm and 52-55 mm categories males represent only 27% and 

 10% of the specimens. The 56-59 mm and 60-63 mm size groups con- 

 tain only females ; no specimens occur between 64 and 75 mm, but the 

 largest B. abyssicola recorded is a male of 75 mm mantle length. 



Such a preponderance of females over males in the larger sizes is 

 curious. Apparently, males do not generally grow as large as females, 

 although the single "giant" specimen at least partially contradicts 

 this conclusion. Males mature early and some may have fully devel- 

 oped spermatophores and packed Needham's sacs at about 25 mm 

 mantle length. All males above 28-30 mm are fully ripe. On the other 

 hand, females generally are not ripe until about 40 mm and often not 

 until 45^8 mm. 



Size differences between the sexes of other adult squid have been 

 noted, primarily in loliginids (review in Roper, 1965). Adam (1952) 

 noted that the males of Illex Ulecehrosus coindetii Avere smaller than 

 the females, and this is borne out in IMS specimens from the Gulf of 

 Guinea. We have also observed, though not tabulated, that males of 

 Ommastrephes fteropus tend to be smaller than females ; none of the 

 numerous large specimens are males. Garcia-Tello (pers. comm.) of 

 the Estacion Biologia Marina in Monte Mar, Chile, informs me that 



