487 



The fully gorged leucocytes, which may be as much as 

 llju, in diameter, begin to accumulate during the last hours 

 of larval life, and the early stages of the pupal period within 

 thecavities of the various appendages. A digestion of their 

 engulfed food occurs here, and soon the food is recognizable 

 only as a number of large rounded or irregular granules within 

 the cytoplasm of the leucocytes (fig. 204). Large vacuoles 

 develop (fig. 194) — structures related porhaps, in some way, 

 to digestion of the granules, and these vacuoles are already 

 quite commonly seen while the leucocytes are still actively 

 engulfing food. Within the cavities of the appendages these 

 vacuoles may increase greatly in size and considerably distend 

 the leucocyte. Frequently the distension is so great that the 

 leucocytes burst (figs. 205, 206), and their nuclei and degen- 

 eration granules float about in the blood stream and finally 

 dissolve. Usually, however, the leucocytes succeed in digest- 

 ing their meal and gradually diminish in size again. The 

 granules slowly disappear, and only small vacuoles remain 

 (figs. 208, 209). In this condition they persist throughout the 

 life of the insect. They are about 7/x in diameter, and have a 

 large nucleus, with a faintly granular chromatic content, and 

 one small karyosome. 



(h) The ''Heart.'' 



The fate of the heart during the insect metamorphosis 

 has, so far as I am aware, never been carefully investigated, 

 and the most contradictory views are held as to the events 

 that occur within it during this period. 



According to Newport, the dorsal vessel of Sphinx 

 ligustri pulsates throughout the whole of the pupal period, 

 and evidently undergoes no changes during this time. In '^ 

 Erisitcdis, on the other hand, Kiinckel d'Herculais observed a 1 

 cessation of the heart beat for one or two days after the eighth 1 

 day of pupal life. — 



According to Kowalevsky (1887) the dorsal vessel in 

 Calliphora pulsates regularly till the third day of pupal life; 

 thereafter it beats more irregularly, but does not seem to 

 undergo any metamorphosis. Lowne (1890-1895) partly in- 

 clines to this view; he observed a change in the form of the 

 heart, but attributed this to a possible replacement of its 

 old muscle cells by new ones, 



Weismann (1864), with no modem technique available 

 to him, came to an entirely different conclusion. He observed, 

 in hand dissections ( !), that the heart became more fragile and 

 was evidently at this time in a state of ''histolysis." "As 

 an organ it is not broken up, but is redeveloped by a process 

 similar to that which has been observed in the intestines and 

 malpighian vessels." 



