DEVELOPMENT OF PHRTGANIDS. 559 



their embryology. One of the earliest references was published 

 by Eathke in Mliller's 'Arch./ 1844. In a footnote (p. 27) 

 he called attention to the increase in the size of the eggs 

 during development. In the posthumous papers of the same 

 author, published by Hagen in the ' Stettiner Entomological 

 Zeitung' for 1861, mention is made of an apparatus for 

 rupturing the e^^ membranes at the time of hatching. Inde- 

 pendently of Zaddach, and, indeed, previous to him, Rathke 

 had also observed the revolution of the Phryganid embryo in 

 the egg, although his notes were not published until several 

 years after the appearance of Zaddach's work. He also des- 

 cribed the general external appearance of the eggs, and their 

 occurrence on the under side of the leaves of water plants, 

 Hydrocaris morsus ranse, Nymphse, and Potamogeton, &c., as 

 well as their arrangement in concentric circles one layer deep. 

 The eggs, one hundred or more in a single cluster, had two 

 membranes, a thick outer chorion, slightly tessellated, and an 

 inner very thin vitelline membrane ; the latter was present 

 when the eggs were first laid, but in subsequent stages was 

 not quite so obvious. 



A faint " Keimhaut " was formed containing nuclei. Deve- 

 lopment was completed in three weeks. Four long and spirally- 

 coiled Malpighian vessels arose behind the stomach. No gills 

 were observed when the larva was first hatched, but thread- 

 like flexible structures appeared later which Rathke supposed 

 to be gills. There was no trace of abdominal appendages. 



By far the most important work on the development of 

 " Phryganids " that has yet appeared is the memoir published 

 by Zaddach in 1854. I will therefore give an outline of the 

 more important conclusions reached by this author. The eggs 

 are found in single layered masses on the under side of the 

 leaves of water plants, and are from *009 inch to 'Oil of an 

 inch in diameter. There are two membranes, an outer, smooth, 

 transparent chorion, and an inner, thin, vitelline membrane. 

 Shortly after oviposition clear spots appear on the surface of 

 the yolk, which gradually increase in number and finally 

 become confluent, forming a transparent outer layer ; this, in 



