THE GENITAL ORGANS — ACARINA. 93 



Kishinotjye's derivation of the coxal glands from an ectodermal invagination 

 winch lengthens into a tube is not only incompatible with their origin in the 

 Scorpion from the mesoderm (p. 24), but also with their relation to the body- 

 cavity. According to Kishtnouye's own statement, the tubular rudiment of 

 the coxal gland opens at its inner end in the shape of a funnel into the coelom, 

 so that the accepted view that these glands are nephridia is confirmed, provided 

 the accounts given are correct. If these glands are ectodermal in origin, then 

 they must be regarded, not as coxal, but as crural glands, and we would expect 

 them to end blindly. Sturany (No. 14), the most recent investigator of the 

 coxal glands in the Arachnida, considers them to be nephridia. If his con- 

 jecture that they end in a terminal sac as in the Crustacea proves correct, the 

 latter would no doubt correspond to a part of the body-cavity. We refer the 

 reader to our account of the coxal glands in the Scorpiones (pp. 24 and 87). 



I. The Genital Organs. 



According to Schimkewitsch, the genital organs arise in the 

 anterior part of the abdomen, within the two longitudinal folds of 

 the splanchnic layer, which have risen up into the yolk from the 

 ventral side. In the median layer of each of these folds an ovoid 

 thickening appears (Fig. 48 ^4). This consists of large central and 

 flat peripheral cells, the latter representing an enveloping epithelial 

 membrane (Fig. 48 B). The anterior end of the rudiment curves 

 round towards the ventral side, and is said to correspond to the 

 efferent ducts, while the rest represents the germ-glands. "When 

 the young Araneid hatches, there is still no communication between 

 the efferent ducts and the exterior ; this is established later by 

 means of an ectodermal invagination (Schimkewitsch). 



[Pueceli, (App. Lit. on Araneae, No. VII.) traces the ducts to tubular growths 

 of the abdominal mesodermal segments ; the openings of these ducts into, the 

 coelom become connected with the genital cells which grow forward from the 

 posterior end of the germ-band. Similar structures develop in all the abdominal 

 appendages, but only those on the second segment persist. He regards them as 

 modified nephridia.] 



VII. Acarina. 



Oviposition. The majority of the Acarina lay eggs, a few (e.g., 

 Halarachne) are said to be viviparous. Some (e.g., Scutovertex) 

 appear to be viviparous at certain times of the year and ovo- 

 viviparous during the remainder of the season, others are habitually 

 ovo-viviparous. The Acarid egg is surrounded by a more or less 

 strong shell, sometimes covered with prominences ; in many species 

 this protective shell is extremely thick and traversed by fine pore- 

 canals.* The eggs are deposited in various places, according to the 



* [According to Trox'ssaet (App. to Lit. on Acarina, No. VII.), the female 

 of Syringobiu chelopus among the plumicolous Sarcoptidae at times reproduces 

 parthogenetically ; the eggs thus produced in the absence of males have no 

 shells. — Ed.] 



