562 WILLIAM PATTEN. 



closing of the " Scheitel Platte ^' to form the brain case and 

 the growth of the " Hautblatt " around the yolk, by means of 

 which the body of the embryo becomes enclosed. 3. The 

 gradual contraction of the germinal folds, by means of which 

 the embryo, hitherto encircling the yolk, now comes to lie with 

 its back turned outward, and, 4, the formation of the mesenteron 

 and all other vegetative organs. 



Just before revolution the '' vitelline membrane " ruptures 

 and collects on the exposed portion of the yolk between the 

 head and tail where it forms a kind of rosette. The author is 

 in doubt whether it forms a part of the dorsal wall or is absorbed 

 by the yolk. The time of the rupture of the vitelline mem- 

 brane varies, and may even be deferred until after the revolu- 

 tion of the embryo. Sometimes the membrane is absent 

 altogether. The under lip is a ridge-like elevation, which is 

 formed from the mandibular and two maxillary segments with 

 the second maxillse as a palpus. 



After revolution, which is caused by the contraction of the 

 ventral side of the embryo, the latter becomes spirally rolled in 

 the egg, and retains this position until hatching. 



The wall of the stomach is formed first on the ventral side 

 and thence grows dorsally. 



The eye first appears as six pigment spots. In some cases 

 the lenses to the compound eye could be distinguished. 



A sharp-pointed organ found on the forehead serves to 

 rupture the egg membranes. The development covered a 

 period of from eighteen to twenty days. 



Previous to Zaddach, Jeder had made some very scanty 

 observations on the nervous system and the eye. 



In 1871 Kowalevsky confirmed Zaddach's observations on 

 the membranes, which, after rupturing, form a kind of rosette 

 on the exposed surface of the yolk between the head and tail of 

 the embryo. These observations were made by Wagner, and 

 communicated by him to Kowalevsky. 



Brandt, in 1878, referring to the formation of a blastoderm 

 in Phryganids described a clear outer layer in which nuclei 

 subsequently appeared. The origin of the cells was not 



