March 1S94.J 



psrcHE. 



43 



tary bees, although additional evidence 

 is needed to establish the sort of para- 

 sitism it is. 



Dr. Packard has reared Notnada iin- 

 hricata Smith anil A', vincta -Say 

 (= pulchella Sm.) from the nests of 

 Andrena vicina Smith; and the 

 former also from the cells of Halictiis 

 parallcliis Say and found : 



Both full-grown larvae and pupae of differ- 

 ent ages, up to the adult Nomada, ready to take 

 leave of its host. It seems, therefore, that the 

 newly hatched young of Nomada must feed 

 on the pollen mass destined for the Andrena. 

 But there seems to be enough for both genera 

 to feed upon, as the young of both host and 

 parasite were found living harmoniously 

 together, and the host and their parasites are 

 disclosed both at the same time. 



Is It n(jt just possible that this socia- 

 bility of the two larvae is fictitious and 

 lasts only just so long as the food 

 supply is sufiicient for both .' When 

 the food supply gives out, will they not 

 also attack each other just as in the 

 case of Stelis.' 



It seems to me that here we have an 

 admirable illustration of the origin of 

 parasitism. We have (i) commensa- 

 lism, (2) parasitism, induced by hun- 

 ger, and (3) genuine parasitisin, which 

 is induced or acquired by the two 

 former conditions, until finally it 

 becomes permanently acquired through 

 heredity. The same thing is strikingly 

 exhibited in the family Cynipidae 

 where we find (i) gall-makers, (2) 

 commensals or inquilines and (3) 

 true parasites, again in the fomily 

 Chalcididae, in the Eurytomides where 



we have (i) gall-makers or plant- 

 feeders {Isosoma and allies), (2) 

 commensals or inquilines {Eitrytonia 

 and allied genera) and (3) true para- 

 sites ( BruchophagHS^ Eui-ytoma, etc. ) . 

 The same state of aflairs occurs also in 

 the fig-insects (Blastophaginae), and 

 in the gall-inhabiting Torymin:ie. 



Family II. Andrenidae. Inhab- 

 its and structure this family is in all 

 respects very closely allied to the pre- 

 ceding. About 150 species, distributed 

 in 14 genera, are already known from 

 boreal North America. 



All of the genera, except the genus 

 Prosapis Fabr., which like Ceratina, 

 in the preceding family, excavates the 

 stems of brambles, etc., burrow gal- 

 leries in the ground in which they 

 place their cells. At one time two or 

 three of the genera, Sphecodes, Augo- 

 chlora and Prosapis, were considered to 

 be parasitic or inquilinous in the cells 

 of some of the others, but have since 

 been shown to be honey-producers like 

 the rest. 



The nests of comparatively few of 

 oin- genera have been studied in detail. 

 Andrena vicina Smith, as observed 

 by Mr. J. H. Emerton and others, ex- 

 cavates a perpendicular gallery in the 

 groimd to the depth of several inches 

 or more, branching off from which it 

 then excavates short oblique galleries 

 in which the cells which are lined 

 with a muscous-like secretion are 

 placed. 



The nests are built in the latter part 

 of April and during May. The cells 

 are then filled with a ball of pollen and 



