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 chelicer®, 

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

 lidium, 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 Gamasus has only two ; but each of these has its own 

 vas deferens. Many Acarina (e.g., Oribates, Bdella, Gamasus) 

 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 Gamasus 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 caecum is a receptacle for the spermatic 

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

 uterus and oviducts. This caecum 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 Oribatidas are viviparous, (Dujardin.) 

 There is no metamorphosis in these animals, except in 

 Sydrachna and Tromhidium. In the latter genus, "the 

 hexapod larvse 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 caeca situated between the so-called 

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



