66 BULLETIN OF THE 



"Within the " chorion " is the structureless vitelline membrane which 

 closely invests the substance of the egg. It is thinner than the chorion, 

 from whicli it is easily separable after maceration. This membrane in- 

 vests mature eggs before they leave the ovarian follicle, and is doubtless 

 a product of the vitellus itself. 



In making sections portions of these membranes were often cut. The 

 vitelline membrane stains faintly in Borax carmine ; the chorion retains 

 its layer of outer granules, which are not dissolved in alcohol. There is, 

 however, no trace of the areal arrangement of these granules, such as has 

 been figured by Ludwig ('76) for Philodromus limbatus. 



The egg is composed of finely granular protoplasm, in which is accu- 

 mulated a large amount of nutritive material in the form of albuminoid 

 yolk corpuscles, and minute fixt globules. The albuminoid material is so 

 distributed as to give the protoplasm a characteristic arrangement. The 

 latter consists of a central mass enveloping the nucleus, a peripheral 

 layer, and a coarse network connecting the two. 



The peripheral layer (couclie germinative of Balbiani) is the most strik- 

 ing feature in the arrangement of the protoplasm. It is in immediate 

 contact with the inner surface of the vitelline membrane, and is so 

 crowded with fat globules that Balbiani concluded erroneously that it is 

 composed exclusively of such globules. 



The central mass of protoplasm forms around the nucleus an irregu- 

 larly limited, spheroidal envelope, containing neither yolk corpuscles nor 

 the fatty globules which are so characteristic of the peripheral layer. Its 

 outer portion is continuous with branching protoplasmic strands, which 

 form a coarse network around the yolk coi-puscles. 



According to the observations of Balbiani the " yolk nucleus " persists 

 during a part, at least, of the embryonic development, and should there- 

 fore be mentioned as one of the constituents of the egg. There is also to 

 be included the perivitelline fluid, which makes its appearance during 

 the contraction of the vitellus. I have no positive information concern- 

 ing the source of this fluid, but having found no evidence of its existence 

 in a definite morphological condition before the contraction takes place, 

 I rest upon the assumption that up to this time it is uniformly distrib- 

 uted through the formative portion of the vitellus. 



