Anatomy and Development of Scorpions. 123 



the follicle it extends down and occupies a diverticulum from 

 the ovarian tube, at the distal end of which the Qg^ is 

 originally formed. I would suggest apoikogenic and katoiko- 

 genic * as, for the present, adequately designating the two 

 modes. The katoikogenic {Scorpio type) forms are always, 

 so far as observation has yet gone, devoid of any appreciable 

 amount of food-yolk. The apoikogenic ones, on the other 

 liand, usually contain a large amount of food-yolk, but, as we 

 shall see, there are certain exceptions [Scorpiops, Vejovis, 

 &c,). In the apoikogenic forms also there appears always to 

 be a double embryonic membrane formed at an early stage, 

 the outer layer of which, usually termed the serous membrane, 

 is easily distinguished by its large cells containing enormous 

 flattened nuclei. I have been unable to find these membranes 

 in the katoikogenic embryos. 



The diverticula at the ends of which the katoikogenic 

 eggs are formed seem always to terminate in a solid cord 

 of cells — the appendix. The central core oE this appendix 

 consists of cells characterized by thick, highly refractive 

 cell-walls and little or no protoplasm. These cells appear to 

 form a means of communication down which the nutritive 

 secretion passes from the outer cells of the appendix to the 

 embryo. The material supplied in this way is usually taken 

 in through the mouth of the embryo, which is one of the 

 earliest structures to be developed. Some of the further 

 specializations for the nutrition of the embryo in these katoiko- 

 genic forms are described below. They form a most interesting 

 series, and, taken along with the forms I have previously 

 described f, seem to afford a good basis for classification. 



A. Apoikogenic Forms. 

 Scorpiops Ilardwickii (Gerv.). 



The embryos of this species appear at first sight quite 

 similar to those of Euscorpius, their position in the ovarian 

 tube being marked in my specimen by oval swellings about 

 2 millim. long and 1 millim. wide. Sections, however, show 

 that while this form agrees with Euscorpius in the place in 

 which the embryo develops, it differs markedly from it in 

 the type of development. We find the inside of the swelling 

 on the ovarian tube lined throughout by a double cellular 



* From anoiKos, away from home, and kutoikos, at home. 



t "Developmentof (S'cw7-»/o/2//w)9es,"Quart. Journ.Micr. Sci. vol.xxxii.; 

 " Some newly-hatched Specimens of Opistkophthalmus," Proc. Roy. 

 Phys. Soc. Edinb. 1896. 



9* 



