No. 2.] THE OVARIAN EGG OF LIMULUS. 173 



has been shown, is probably a product of the epithelial cells, 

 being a secretion of the protoplasm of the basal end of these 

 cells (PL XIV, Fig. 19, t.p.). 



The larger ovarian eggs offer excellent opportunities for the 

 study of this tunica propria. When removed from the egg, 

 and viewed in optical section under the microscope, it is seen 

 to be a homogeneous membrane, without cell boundaries and 

 without nuclei. It is, however, studded with closely-set shin- 

 ing dots, as if perforated with closely-set pin holes (PI. XIII, 

 Fig. i8,/>.c.). The nature of these becomes sufficiently evi- 

 dent when the formation of the egg membrane is examined. 



There being no true follicle epithelium surrounding the egg, 

 the coverings, which in later stages make their appearance, 

 arise from the egg itself. On account of the considerable 

 development of this covering, I shall follow Packard and Kings- 

 ley and call it the chorion, being aware that, according to the 

 nomenclature adopted by Ludwig and van Beneden, we should 

 be obliged to call it the vitelline membrane. 



The chorion is a product of the egg. In the living egg it 

 has a semi-solid consistency and offers considerable resistance 

 to pressure. It may be ruptured by inserting a needle and 

 severing it in that way. In so doing, it may be drawn out to a 

 sharp point somewhat like india-rubber ; but, unlike rubber, it 

 does not return to its former position. Fresh eggs examined 

 in glycerine or normal salt solution often show the formation 

 of extraovates, without the rupture of the membrane. 



E.xamined in the living state, the chorion is seen to consist 

 of one or several concentric layers according to the size of the 

 egg (PI. XIII, Figs. 12, 13, 17, 18). Each layer is uniform in 

 thickness ; but considerable variation may exist between the 

 different layers. The layers appear to consist of a dense sub- 

 stance, between every two layers of which there is a thin- 

 ner lamella of lighter, apparently less dense substance. These 

 layers of darker and lighter substance are not clearly separated, 

 but grade into each other. Preserved in most hardening rea- 

 gents, the chorion becomes hard and brittle, offering in the 

 mature egg considerable resistance to the entrance of paraffine 

 or celloidin. In such preparations the lamellae may also be seen ; 



