REPRODUCTIVE SYSTEM. 115 



able form and surrounded by a muscular layer. It opens 

 into the vagina below the point of junction of the two ovi- 

 ducts, by means of a canal of variable length. The seminal 

 vesicle is empty, except after copulation, when it always 

 contains a multitude of spermatozoa moving very actively: 

 these movements are kept up for a long period. The secre- 

 tory glands, situated at the lower end of the vagina, con- 

 sist of two rather long glandular tubes on each side of the 

 vagina, into which they open, either directly or through two 

 small special excretory ducts. They often have on their 

 course two vesiculiform reservoirs. The male organs recall 

 the general plan of the female. The vas deferens, ordinarily 

 simple, may have at its lower extremity a vesicular dilata- 

 tion (vesicula seminalis); at their point of junction on the 

 ejaculatory duct there are usually two longer or shorter 

 simple mucous glands, which secrete a quickly coagulating 

 granular mucus, which serves, during the copulatory act, 

 partly to fill and distend the copulatory bursa and partly to 

 surround portions of the sperm, and thereby form spermato- 

 phores. (Siebold.) A variety of copulatory organs are seen, 

 most generally modifications in last segment of abdomen or 

 chitinous deposition in terminal portion of vas deferens, and 

 often protruded through agency of complicated muscular ap- 

 paratus. "With Libellula (dragon-fly), the opening is simple, 

 being covered by two very small oval valves. The seminal 

 vesicle is placed in a depression at the base of the abdomen. 

 Under sexual excitement the male fills the vesicle (which, 

 owing to the flexibility of the abdomen, is readily accom- 

 plished) and secures the female about the neck by the anal 

 claspers. He remains passive during coition, which is ac- 

 complished by the female placing her genital pore in con- 

 nection with that of the vesicle. 



Arachnida. Sexes distinct, except in Tardigrada. Ovaries 

 or testicles double, blended together on the median line; 

 they have two excretory ducts which open by a single pore 

 at the base of abdomen or under the thorax. Rarely is there 

 an ovipositor or penis as in Phalangidae. Accessory glandules 

 to the oviduct or vas deferens do not differ essentially from 



