NO. 3 EMBRYOLOGY OF FLEAS KESSEL 1 1 



superficial protoplasm and difficult, therefore, to demonstrate. Such 

 a covering, if present, would lie inside of the vitelline membrane and 

 would be evident when the germ cells push out at the posterior pole 

 as described in a later section. Such a membrane is not apparent in 

 flea eggs. 



The superficial protoplasm of insect eggs is known as the periplasm 

 or cortical ooplasm. The periplasm at the anterior pole is called the 

 anterior polar plasm, and that at the posterior pole is termed the 

 posterior polar plasm. In the eggs of many forms either one or both 

 of the polar plasm regions are widened to form protoplasmic caps 

 which some authors regard as adaptations to facilitate the entrance of 

 spermatozoa. As will be described later in the section on germ cells, 

 most writers on insect embryology believe that the posterior polar 

 plasm plays an important role in the differentiation of the primordial 

 germ cells. In comparison with the eggs of most other insects, those 

 of fleas possess a very narrow periplasm, and none of the sections 

 made during this investigation showed it widened to form an anterior 

 protoplasmic cap. However, some of the sections have this cortical 

 ooplasm perceptibly thickened at the posterior pole (pi. 5, fig. 43). 

 The entire periplasm is uniiormly granular and no darker-staining 

 granules are in evidence in this posterior protoplasmic cap. 



The periplasm is continuous with an anastomosing reticulum of 

 protoplasmic strands which ramifies throughout the inner portion of 

 the egg. Contained within the meshes of this reticulum are numerous 

 vitelline spheres which make up the deutoplasm or store of yolk for 

 the nourishment of the developing embryo. These vitelline spheres 

 vary considerably in size. Lying within each of them are several small, 

 rounded, and refringent bodies. These are the vitelline bodies. Both 

 vitelline spheres and their vitelline bodies appear in many of the 

 accompanying photomicrographs (pi. 1, figs. 4, 5, 8, etc.). Delafield's 

 haematoxylin was found to leave both the vitelline spheres and vitelline 

 bodies colorless, and was used for the sections from which the above 

 illustrations were made. By contrast, Heidenhain's iron haematoxylin 

 stains both structures black (pi. 1, fig. 13). 



Multitudes of granulelike objects, apparently identical with the 

 granules of the periplasm, may be present along the strands of the 

 protoplasmic reticulum (pi. 5, fig. 45). These are by no means uni- 

 formly distributed, and their concentration varies in different prepara- 

 tions. They appear to correspond to the Blochmann's corpuscles which 

 have been observed in the eggs of certain other insects. These bodies 

 were first observed by Weismann (1863), and, although he includes 

 a short discussion of the development of the dog flea egg in this 



