70 PETER OKKELBERG 



The change may take place in some cells when the larvae are less 

 than 40 mm. long; while in other larvae no oocytes are fomid 

 until a much later stage, in some cases not until the larvae are 70 

 mm. long. Few or many growing oocytes may form in the germ 

 gland in very early stages. In most cases they are formed before 

 the larvae are 70 mm. long, at which stage the sex glands are 

 either predominantly male or predominantly female. A few 

 oocytes may enter the growth phase after the larva is 70 mm. 

 long, especially in glands that are predominantly male. After 

 that time the cysts and undifferentiated germ cells gradually 

 disappear in larvae destined to become females, while in those 

 that become males the oocytes which have reached a considerable 

 size or which may form in the gland subsequent to this time 

 remain in the gland up to the adult stage. One such cell from an 

 adult testis is shown in figure 63. It has been found that in the 

 majority of adult testes such undeveloped oocytes occur. 



Although the caudal portion of the germ gland remains smaller 

 and less developed than the cranial portion, yet no difference 

 has been found in the structure of the glands in the two regions. 

 The tendency to form oocytes seems to be equally strong in the 

 cranial and caudal portions of the gland. 



So, whether the germ glands eventually become ovaries or 

 testes, they all develop oocytes, and this is an undoubted female 

 character. Sometimes only a few oocytes are present, and again, 

 with the exception of a few indifferent germ cells scattered through 

 the gland (singly or in cysts), oocytes may make up the whole of 

 it. Hundreds of glands from young larvae have been examined 

 to ascertain whether or not there are, in addition to the oocytes, 

 any other sex characters which might indicate that the larvae 

 are predetermined to form one or the other kind of sexual indi- 

 viduals, but none have been found. The germ glands vary some- 

 what in different regions, the result of the presence of blood- 

 vessels and the irregular distribution of the various somatic 

 elements, but the limits of such variation of the somatic parts of 

 one gland are not appreciably different from those of any other 

 gland. The only basis, therefore, for considering a larva male 

 or female is the relative number of cysts and oocytes present in the 



