128 BULLETIN OF THE 



have found less serviceable than the stains above mentioned. After 

 staining, the preparations were dehydrated, cleared with oil of cloves, 

 and mounted in benzole-balsam. 



The embryo is enveloped by three epithelial membranes, the ovarian 

 capsule, the membrana serosa, and the amnion, — named in order from 

 without inward. 



The serosa and amnion are strictly embryonic structures, analogous 

 to the foetal membranes of the higher Vertebrates. There are two 

 contradictory accounts as to the manner of their formation. Possibly 

 they do not arise in the same way in all genera of scorpions. In a 

 brief communication by Kowalevsky uud Schulgin ('86, p. 526) upon 

 the development of Androctonus ornatus, it is stated that they originate 

 as a fold from the edge of the blastoderm, the outer layer of the fold 

 forming the serosa, the inner the amnion. The fold grows up over the 

 blastoderm, the edges coalesce, and the membranes finally separate from 

 the ovum. The more recent account by Laui-ie ('90, p. 114) states that 

 in Euscorpius the serosa arises by a proliferation of the peripheral cells 

 of the blastoderm, extends as a delicate membrane forward and back- 

 ward over the egg, which it finally covers completely, and then becomes 

 entirely separate from the blastoderm. The formation of the amnion 

 begins when the serosa has covered about two thirds of the embryo, and, 

 like the serosa, its origin is ectodermic. The amnion, however, " never 

 loses its connection with the epiblast as the serous membrane has now 

 done, but remains attached to its edges and only extends round the 

 egg as the epiblast extends" (p. 116). Unfortunately, I have not 

 obtained sufficiently early stages of Centrurus to ascertain how its mem- 

 branes arise, but, in removing the latter from the embryo, I have never 

 found the amnion attached to the ectoderm. The membrane which I 

 have called the " ovarian capsule " I at first wrongly took to be the 

 follicular epithelium, and under this supposition it was indicated as e'th. 

 fol. in Figure 2. Like the follicular epithelium, it arises from the 

 ovarian tube ; but the follicle is formed as a diverticulum of the tube, 

 previous to the maturation of the ovum, and serves as a nutritive cap- 

 sule for the latter during its growth. The ovarian capsule, on the 

 contrary, is that part of the ovarian tube which receives the ovum after 

 fertilization, and enlarges to accommodate the growth of the embryo. 



The fcetal membranes fit so loosely over the embryo that they can be 

 easily removed in a single piece. In late stages, the ovarian capsule is 

 readily sepai'able from the membranes ; in earlier stages, it adheres closely 

 to them. It is rarely possible to separate the serosa from the amnion. 



