REPRODUCTION AND SEX 535 



other into expression or development, is afforded by the metaboUsm 

 conditions that have been set up in the cytoplasmic field of opera- 

 tions, which lead also to the establishment of spermary or of ovary, 

 as the case may be. 



It may also be noted that in thinking of the general question 

 of the Determination of Sex, we are probably on safer ground when 

 we pass from the higher animals with their highly specialised 

 dimorphism — familiar in peacock and peahen, ruff and reeve, lion 



Fig. 79. 



Male of Paper-nautilus (Argonauta). After Jatta. A shows the ordinary arms 

 (OA) and a much modified arm laden with spermatophores within a 

 "hectocotylus sheath" (HS). E, eye; MMC, mantle cavity; F, funnel. 

 In the lower figure (B) the transformed arm (HA) has been much 

 elongated beyond the sheath. 



and lioness, man and woman — and get down to the lower reaches 

 where, as in starfishes and sea-urchins, it is often impossible to 

 distinguish the two sexes without a microscopic examination of the 

 reproductive organs. 



It is profitable to press the problem further back to its simplest 

 expressions, such as we see, for instance, in Volvox, that beautiful 

 sphere of flagellate cells which so well illustrates a body in the 

 making. From the ball of cells reproductive units are sometimes set 

 apart, which divide to form other colonies without more ado. But 

 in other conditions, when nutrition is checked, a less direct mode of 



