ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 29 



The reproduction of 31. acervorum is purely parthenogenetic, that of 

 31. americana purely amphigonous. The receptaculum seminis and the 

 gland ulae ductus receptaculi in 31. acervorum do not, however, show 

 signs of becoming rudimentary. It is probable that in some species 

 there is partial parthenogenesis associated with less frequent amphi- 

 gonous reproduction (31. ochracea, 31. nebracensis). Oviposition in 

 31. acervorum, and probably in other species also, takes place within the 

 nest of the host. The eggs are few in number, but of large size ; they 

 develop in about six weeks. Oviposition may take place at any time 

 except during the winter months. 31. acervorum may pass the winter 

 in the nest of the host either as an imago or in the larval state. The 

 usual duration of life is two years. This species (and probably others, 

 also) follows its hosts when they change their nests. The crickets, like 

 the ants themselves, are guided by their sense of smell. In regard to 

 structure, the oval-shaped body and the leaping legs may be considered 

 as adaptations securing the necessary rapidity of movement ; the 

 thickening of the antennas and cerci, the widening of the antennal pits, 

 and the thickening of the maxillary palps, as adaptations to the mimetic 

 association with ants ; and the hypopharyngeal tufts and hypopharyngeal 

 ducts as adaptations for licking up the food. The parasitic habit has 

 resulted in an increase in size of the head and intestine, and a slight 

 dwindling of the proventriculus ; while the rudimentariness of the 

 dioptric apparatus of the faceted eye is probably due to the subterranean 

 life. The small number of eggs, the size of the egg, and its abundant 

 yolk-supply, are consequent on the diminished selection conditioned by 

 the parasitic habit. 



Eyes of Dactylopius.* — F. H. Krecker has made a study of the 

 common mealy bug, Dactylopius destructor, with a view to throwing 

 some light on the abnormal condition presented by the family Coccida? 

 in regard to the number, condition and position of the eyes. He finds 

 that the adult Dactylopius has three pairs of eyes, two accessory and 

 one primary. The latter are bead-like, and lie on the ventral surface of 

 the head. Of the former, an oval pair lies on the ventral surface, and a 

 circular pair on the dorsal surface of the head. The accessory eyes have 

 a large circular lens, followed by a comparatively thin layer of corneal 

 hypodermis, encircling which is a single row of large iris cells. Below 

 this there is a crescent-shaped area of polygonal rods, which are 

 terminally situated on the retinal cells, and are separated from one 

 another by a seam of denser material enlarged at its basal end. There 

 is no grouping of rods or of retinal cells. From the proximal end of the 

 retinal cells extend the nerve fibrils which join to form the optic nerve, 

 which follows the contour of the head to enter the brain laterally. 

 Reddish-brown pigment fills the retina, the iris, and also a ridge 

 surrounding the eyes. There are no cells which function as pigment- 

 cells alone. 



The primary eyes are extremely small. They have no corneal 

 hypodermis, no visual rods, no iris. There is a lens below which are a 

 few retinal cells. The nerve fibrils leave the cell proximally, and the 



* Zeitsehr. wiss. Zool., xxxix. (1909) pp. 73-S9 (1 pi.). 



