ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 209 



the integument, one on each foot-bearing segment ; their centre is 

 occupied by about 100 glistening bodies, which are the truncate 

 ends of a corresponding set of conical mouth-pieces belonging to long 

 ducts, each of which leads from a long pyriform gland. This gland 

 is called unicellular by Passerini ; its basal membrane, which is very 

 thin, contains a number of smooth and striated fibres, which ramify, 

 anastomose, and form a reticulum, and are connected similarly with 

 those of the neighbouring glands, and extend over the ducts. The 

 larger fibres, some of which measure 0*012 mm. in diameter, start 

 from common centres. The fibres very often exhibit a succession of 

 slight inflations, and are evidently contractile and intended to 

 compress the gland and expel its contents. The system of glands 

 belonging to one segment is invested by a delicate membrane con- 

 taining weak fibres and surrounded by adipose cells, and is innervated 

 by nerve-branches derived from the anterior nerve of the pair which 

 is given off on each side by the ganglion of the segment ; the trachesB 

 belong to a branch which comes direct from the main trunk. 



The liquid contained in the gland coagulates promptly in the air, 

 has an acid reaction and taste, and irritates the tongue, is soluble in 

 water and alcohol and becomes whitish under the action of caustic 

 potash; the coagulum shows under the Microscope an amorphous 

 mass containing elongated crystals, which generally form rosettes 

 about • 14 mm. in maximum diameter ; analysis shows its composition 

 to be analogous to that of silk. The only direct evidence as to the 

 function which the author was able to obtain was that when the back 

 is mechanically irritated, the animal turns up its ventral surface, and 

 the disks become covered with the fluid, the object of which seems to 

 be retaliation. 



7- Araclinida. 



Polymorphism and Parthenogenesis in Acari.* — A. Berlese 

 states that the adult Gamasus, like all parthenogenetic forms, produces 

 viviparously hexapod larvae ; from these are produced nymphs, which 

 never develope ova till they reach the mother-stage. Both the larvae 

 and the nymphs are distinguishable by their soft hyaline epidermis, 

 and the complete absence of any reproductive organs. There are 

 nymphs which ought to become males, and others which should become 

 females ; and this, which is the most frequent arrangement, may be 

 spoken of as the normal series. In addition, there are individuals 

 which cannot be produced by the adults or the higher forms of the 

 series, but they are derived from two distinct groups, which, like the 

 adults, are of the ordinary, or of the extraordinary series. On the 

 other hand, the higher forms may be derived by metamorphosis from 

 lower forms of the extraordinary series. Thus G. tardus produces a 

 special larva from which, by rapid metamorphosis, there is developed 

 a larger, octopod nymph. During the whole of its development this 

 form is octopod and asexual; it moults as it grows, but does not 

 seriously alter in form ; at the later moults a slight difference may 

 be detected between the future males and females, but there are no 

 traces of any secondary sexual characters. 



A detailed account is given of the metamorphosis of G. tardus, 



* Arch. Ital. Biol., ii. (1882) pp. 108-29 (1 pi.). 

 Ser, 2.— Vol. III. P 



