'300 Annals Entomological Society of America [Vol. Ill, 



membrane and striate border and in time the nidi take on their 

 normal condition and the new epithelium is mature. Here we 

 find the epithelium cast off Ijodily and not merely in part. In 

 conclusion IMobiisz maintains that: 



(1) At each larval molt there is a total regeneration of the 

 epithelium of the mid-intestine, 



(2) The transformation of the mature larva to the pupa, 

 in the holometabola, is simply an intensified larval molt and we 

 may expect the same morphological changes, although to vary- 

 ing degrees, perhaps, at these periods. 



(3) He believes that there is not only total regeneration 

 of the mid-intestinal epithelium but also that there are greater 

 or less changes in the epithelium of the fore- and hind-intestine 

 and in the muscular and adipose tissues of the larva. 



The larva of Psychoda alternata on preparing to molt, 

 ceases feeding for a short time and to a marked degree dis- 

 charges the food content from the alimentary canal. Then 

 comes a short period of inactivity followed by pronounced 

 peristalic contractions. In. the thoracic region a strong ven- 

 tral flexure occurs and then peristaltic waves of contraction pass 

 forward from the posterior end of the body. This may be 

 repeated a number of times before the chitin bursts on the dor- 

 sum of the first two thoracic segments and the larva crawls out. 

 As soon as the larva is free it becomes quite active and begins 

 to feed. These outward signs of transformation are simply the 

 culmination of the metamorphosis. The internal changes are 

 practically completed before the larval skin is cast. 



Shortly before the time of molting the mid-intestinal epi- 

 thelium begins to undergo striking changes. The cells begin 

 to elongate and protrude into the lumen. Their distal halves 

 become distinctly vacuolate (Fig. 48). There is to be noted 

 in the nuclei themselves some change. The chromatin usually 

 disappears or comes to closely envelope the nucleolus. At this 

 stage the cytoplasm and enclosed secretions of the cells stain 

 intensely with iron haematoxylin which can be removed only 

 by ])rolonged differentiation. 



This stage in the metamorphosis was first observed in a 

 larva that had fasted for three days and was thought to be due 

 to the storing up of digestive secretions, but when other speci- 

 mens from the same lot were examined and no signs of such 

 development found and when larvae, that were known to be 



