DEVELOPMENT OF PHRYGANIDS. 563 



observed^ but in harmony with his theory he believes that they 

 are direct descendants of the germinal vesicle. 



Dohrn^in 1876, also noted the rupture of the membranes and 

 the formation of a dorsal organ. He says that it finally dis- 

 appears, but does not state in what manner. 



IV. Descriptive. 



Stage 1. — In this stage will be included an account of the 

 egg from the time it is deposited until the formation of 

 blastoderm. 



The youngest eggs observed were usually ovate in out- 

 line, and often more or less irregular from mutual pressure. 

 The viscid, greenish yellow yolk completely fills the chorion 

 and contains two kinds of rounded elements ; those of one 

 kind are albuminoid in nature, staining deeply in all the 

 common reagents; those of the second kind are colourless, 

 much more refractive than the first, and exceedingly variable 

 in size. They are dissolved in the processes preceding im- 

 bedding, so that in sections their former existence is indicated 

 only by the presence of circular cavities in the yolk ; from this 

 it is to be inferred that they are oil globules. 



Within ten or or twelve hours after oviposition, the time 

 varying with the temperature, a clear space makes its appear- 

 ance at the surface of the egg, and gradually increases until 

 it has attained the breadth of the future blastoderm. In this 

 layer, which has been called the " blastema," ^ the protoplasm 

 has, under ordinary conditions, a very homogeneous appear- 

 ance, with occasionally lighter, less refractive spots which 

 appear like vacuoles, but in which, when observed more closely 

 and under slight pressure of a cover-glass, or especially when 

 treated with a very little acetic acid, faintly marked nuclei 



' There is not the slightest doubt that in many insects a structure precedes 

 the true blastoderm, presenting many well-defined characteristics which 

 distinguish it from the blastoderm ; hence it requires a special name. I can 

 see no objection to retaining the name "blastodermic blastema," or simply 

 " blastema," originally proposed by Weisman, even though his view that the 

 nuclei of the blastoderm arise in this layer spontaneously is incorrect. 



