262 MEDICAL ENTOMOLOGY 



from the early stage up to the time of oviposition, tabulates the 

 process and divides the successive changes into live stages as 

 follows : 



Stage 1. Follicle consists of a group of undifferentiated cells. Follicle 



and central cells become differentiated. 

 Follicle cells form a distinct epithelium, like cubical 



epithelium. 

 Follicle becomes oval. 

 Nucleus of the ovum becomes distinguished from those of 



the nurse cells. 

 Stage 2. Fine yelk granules appear in protoplasm of ovum. 



Coarse yelk granules appear and increase greatly in number. 

 Ovum increases relatively to nurse cells until it occupies 



half the follicle. 

 Stage 3. Nucleus is obscured by yelk. 



Ovum occupies , , and f respectively of ovum. 

 Stage 4. Follicle becomes elongated. 



Nurse cells become less and less conspicuous. 

 Follicle assumes shape of mature egg. 

 Stage 5. Floats and chitinous structures become visible. 



Egg is laid. 



Since the second follicle commences to develop before the first is 

 ripe, the ovary is only found in the first stage in the case of a 

 female which is about to develop the first batch of eggs. After 

 laying the first batch the ovary is at the second stage, and there- 

 after there is nothing to indicate how many batches of eggs have 

 already been matured and deposited. Certain other points are of 

 assistance in determining the age, or rather in separating the very 

 young specimens from the rest. The salivary glands are in an immature 

 stage for the first twelve hours of the life of the imago. The 

 spermathecae nearly always contain sperms beyond the first stage. 

 The mid-gut is practically never free from blood after the first feed 

 except when the ova are nearly ripe, and one may conclude, therefore, 

 that an anopheline without any blood in its mid-gut and with ovaries 

 in the second stage has just laid a batch of eggs, and has not fed 

 since it did so. Occasionally one or two ova are retained while the 

 rest of the batch are deposited, and the presence of these retained ova 

 is proof that the specimen has laid at least one batch of eggs. 



From laboratory experiments carried out at Amritsar in July, Chris- 

 tophers found the rate of development to be as follows : 



