612 ROBERT n. BOWEN 



Gallosamia (where it was observed by Cook (1910)) this body 

 seems to appear very early (fig. 44), but in Pygaera it 

 becomes conspicuous only in later stages. In the latter it can 

 be recognized as a minute granule at the time when the elonga- 

 tion of the nebenkern is well started (figs. 4, 8, and 13), and 

 subsequently (figs. 15 to 18) it becomes larger and much more 

 prominent. In Gallosamia it may divide into two parts 

 (often unequal) at a fairly early period (fig. 46). In Pygaera 

 the division is delayed until the clear area (in which it tends to 

 be located (figs. 20 and 22)) in the head is differentiated, and 

 when it does occur, it tends to take place in all the heads of 

 a cyst (figs. 19 and 20). In later stages this body seems to 

 become less conspicuous (figs. 31 and 35), and, I believe, 

 eventually disappears entirely, being presumably dissolved 

 in the nuclear sap. Not infrequently this body is in hne with 

 the tail filament, and it might easily be mistaken for a centriole 

 (figs. 52 and 57). As far as I can make out, however, it has 

 no real connexion with an}- extra-nuclear structure. 



Finally, I would like to mention in passing a phenomenon 

 which seems to have been overlooked by previous workers on 

 Lepidoptera, and wliich I myself do not fully understand. An 

 examination of cysts of sperms in later stages of transformation 

 (figs. 36 and 58. for example) shows the elongated acrosomes to 

 be embedded in a mass of large, clear vacuoles which have 

 the appearance of a large number of soap bubbles crowded 

 together. I supposed at first that these vacuoles represented 

 an elaboration of the protoplasm of the so-called nurse-cell 

 in which the sperm heads of insects are characteristically 

 embedded. Further study indicated that this view was not 

 tenable, for at a slightly earlier stage more or less separated 

 vacuoles could be found among the heads without any apparent 

 connexion with cells of the cyst wall. I would like to suggest, 

 as a possible explanation of their origin, that these vacuoles 

 represent material extruded from the nucleus probably at the 

 time of its diminution in size, and comparable to the similar 

 extrusions which seem to occur in the Hemiptera (see Bowen, 

 1922 a) and other animals. This view is borne out by the 



