ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 345 



cells of the embryo. The larvae at the later stage break away from 

 their membranes and are free-living for a time. They afterwards eat 

 up nearly everything in the host-caterpillar's body and then pupate 

 (usually inside, in some cases apparently outside) the body of their host. 

 Broods may be purely female, or purely male, or mixed (from several 

 ova). As far as is known, fertilized eggs develop into females, unfer- 

 tilized into males. 



In discussing these facts established by various investigators, Gatenby 

 comes to the following conclusions : — 1. The " germ-cell determinant," 

 being possibly a nutrient cytoplasmic mass, has no other effect than that 

 of temporarily stopping mitosis in the cells which happen to contain it. 

 There is no evidence for supposing that the "germ-cell determinant" 

 cells form the germ-cells of each embryo. 2, There is absolutely 

 no evidence in polyembryonic species of a " germ-track." Everything 

 is, in the first place, subservient to the production by haphazard divisions 

 and fragmentations, of numerous morula, without any discoverable 

 definite regions. Differentiation of germ-layers follows later. Mere 

 position in the morula is all that seems to determine whether this 

 or that cell will be an ectoderm or endoderm cell, and so on. J, A. T. 



Insect Parasites of some Coccidse. — A. D. Imms {Quart. Journ. 

 Micr. Set., 1918, 63, 293-74, 31 figs.). An account is given of 

 Blastothrix hritannica Gir., and Aphycus melanostomatus Timb., two 

 important Chalcid parasites of the scale-insect, Lecanium caprese, which 

 is widely distributed in England, especially on hawthorn. There are in 

 the year two generations of B. iritannka ; males and females occur in 

 approximately equal numbers ; the first generation of adults are derived 

 from hibernated larvte and emerge during May and early June. The 

 female lays one Qgg, or several eggs in the young fully-grown host, per- 

 forating the body-wall and leaving the pedicel of the egg projecting on 

 the exterior. The newly hatched larva is unique among Hymenoptera 

 in being metapneustic ; its spiracular extremity remains attached to the 

 chorion of the egg, so that free air is available. Later on it loses this 

 attachment and becomes peripneustic with nine pairs of open spiracles. 

 It lies free in the cavity of the body of the Coccid ; it may be enclosed 

 in a phagocytic sheath. Pupation occurs in the host. One host may 

 harbour forty-two pupge. 



The second generation of adults emerge in greatest numbers during 

 the first three weeks of July. The females utiUze the very young larval 

 Coccid hosts for purposes of oviposition, and lay an egg in each. The 

 larva3 remain through the winter with their hosts an^ pupate, as a 

 mle, during the following April. 



In A. melanostomatus there are also two annual generations. Males 

 occur in the approximate proportion of 1:3 females. The first 

 generation of adults emerges between the beginning of May and the 

 end of June. The eggs have no pedicel. The newly hatched larvee 

 are apneustic, respiration being cutaneous. They afterwards become 

 peripneustic with nine pairs of open spiracles, and are usually enclosed 

 in a sheath or cyst. Pupation occurs within the host ; there may be 

 1 to 18 pupa3 in one. 



