440 PHYSIOLOGY OF THE INVERTEBRATA. 



instance, consist of a group of five pairs of follicles which 

 unite in the abdomen. There are two vasa deferentia which 

 terminate in the base of the so-called chin-like process. The 

 male introduces this process, together with the cheliceras, 

 into the vagina of the female during copulation. In Trom- 

 hidium, the testis consists of twenty follicles attached to a vas 

 deferens which opens between the posterior legs. Although 

 there are twenty follicles comprising the testis of Tromhidium, 

 that of Gamasiis has only two ; but each of these has its own 

 vas def ex-ens. Many Acarina (c.fj., Orihatcs, Bddla^ Gamasns) 

 possess a penis, which is situated in a similar position to that 

 of the vulva of the females. As accessory organs of repro- 

 duction, some of the legs are used by the males to retain the 

 females during coition. The female organ consists of a pair 

 of ovaries, whose ducts open in a common vulva situated, as a 

 rule, in the middle of the abdomen on the ventral side of 

 the body. In Gmnasus and Ixodes^ the genital aperture is 

 situated on the thorax. The two oviducts of Ixodes ricinus 

 open into a pyriform uterus, whose neck, according to Von 

 Siebold, communicates laterally with a large ceecum coming 

 from the vulva. The c^cum is a receptacle for the spermatic 

 fluid during copulation ; which, after the act, flows into the 

 uterus and oviducts. This ca3cum is also in connection with 

 two small glands, filled with transparent cells, which secrete a 

 substance for enveloping the ova. 



The oviduct of many Acarina opens into a protractile 

 ovipositor — an organ used in depositing the ova under the 

 epidermis of animals or plants. Most of the Acarina are 

 oviparous, but the Orihatida: arc viviparous. (Dujardin.) 

 There is no metamorphosis in these animals, except in 

 Hydrachna and Tromhidiuni. In the latter genus, " the 

 hexapod larva? are attached to flies, grasshoppers, plant-lice, 

 and various other terrestrial insects." 



In the Araneina the sexes are distinct. The testis of the 

 male consists of two long ca3ca situated between the so-called 

 " hepatic " lobes ; and from them lead two vasa deferentia 



