208 Annals Entomological Society of America [Vol. XI, 



Circular muscles. The circular muscle fibres are well 

 developed and lie in the connective tissue sheath outside that 

 of the longitudinal fibres, this sheath being continuous with 

 that of the mid-intestine. There are thus in the ileum two 

 connective tissue sheaths around the canal outside the basement 

 membrane of the epithelium. 



FORMATION AND ATTACHMENT OF THE BLADDER. 



" The four IMalpighian vessels (those of the first series) whose 

 fusion at their proximal ends is to form the bladder, run closely 

 parallel to one another between the ventriculus and the ileum, 

 for some little distance before they unite. At the point of 

 fusion there is at first no change in the character of the cells, 

 and an ovoid swelling is formed without any interruption of the 

 separate lumen of each tube. The two outer vessels (i. e., the 

 two nearest the ileum) unite first, and their combined lumen is 

 lined with very small epithelial cells, with a faint striated 

 border. The other two vessels are arranged at right angles 

 to them, with their lumina still distinct, and their cells of the 

 usual size. Here as elsewhere the whole enlargement is invested 

 with a basement membrane and a nucleated peritoneum dis- 

 tinct from the former. The cells of the two inner vessels 

 become smaller abruptly, and in a few sections of six micra 

 each, an uniform bladder results, with a common lumen (made 

 up of the fused lumina of the four vessels) lined by a single layer 

 of epithelial cells. The striated border, faint everywhere in the 

 fusing vessels, has now disappeared and is replaced by a thin 

 intima. In some cases the epithelium seems to consist of more 

 than a single layer, but this is only apparent, not real, and is 

 due to folding. The cell divisions are never clearly distinct. 

 The nuclei of the bladder cells are of the same essential structure 

 throughout, although they vary greatly in size, according to 

 the size of the cells. They are round in the larger cells, and 

 ovoid or oval in the smaller. They are densely chromatic and 

 stain intensely ; the chromatin is in the form of coarse granules 

 with a few larger periferal granules in each nucleus. 



As the bladder approaches the ventriculo-iliac bend, the 

 circular rtiuscles of the intestine grow out and surround it, and 

 the lumen of the bladder soon opens directly into that of the 

 proximal portion of the ileum. The intima of the bladder, 

 both primary and secondary, is directly continuous with that of 



