DEVELOPMENT OF PHRYGANIDS. 5G5 



the protoplasm has an undulating outline, showing the first 

 indications of division of the syncytium into distinct cells. At 

 this period also no nuclei are to be seen in the yolk. The 

 explanation of these facts is very simple. The nuclei first seen 

 in the yolk have arisen by the division of the germinal 

 vesicle, and together with the protoplasm scattered through 

 the yolk are migrating towards the surface. In the later 

 stages it will be observed that all the germ cells have reached 

 the surface, forming a syncytium, the blastema, which speedily 

 develops into the blastoderm. 



There is considerable variation in the relative amount of 

 protoplasm and the number of nuclei which may be found at 

 the surface at a given time. Very often the protoplasmic layer 

 would attain a thickness equal to that of the future blastoderm, 

 and yet contain but a very few scattered nuclei; while, on the 

 other hand a large number of nuclei could be seen at the 

 surface, where there was hardly enough protoplasm to form a 

 continuous layer. Hence it is not only possible, but also 

 probable, that a blastema might in some cases occur in which 

 there were no nuclei. For if in one species, as in Neophalax, 

 we can have a blastema containing a very few or a great many 

 nuclei, it is not improbable that in other insects the variation 

 may be carried a step farther and produce a layer of protoplasm 

 in which there are no nuclei. Such a modification would be 

 of extremely slight morphological value, since it is a condition 

 which is dependent on the fact that sometimes the protoplasm 

 reaches the surface first, and sometimes the nuclei. We have, 

 however, seen that such variations can actually exist in one 

 species. Still, the fact remains to be proved by means of 

 sections that a blastema actually does exist without nuclei. 



The yolk^ presents two varieties ; in one the globules are 

 perfectly homogeneous, and stain deeply ; in the other they 



* The greater part of this section on the structure of the yolk applies 

 chiefly to Blatta, on which the most complete observations were made. 

 From what was seen in Pliryganids, I should think that the same description 

 would apply to that group also. In Phryganids the yolk is not so compact, 

 and the amount of protoplasm is proportionately much larger. 



VOL. XXIV. NEW SEll. Q Q 



