39^ THE INVERTEBRATA 



advantage accruing from this greatly increased reproductive capacity 

 is obvious 



Parthenogenesis is in certain cases, chiefly in the family Cecido- 

 myidae of the order Diptera, found to occur in larval forms. In 

 Miastor, a form living in decaying wood and bark, reproduction in this 

 manner (paedogenesis) occurs for the greater part of the year. These 

 larvae contain prematurely-developed ovaries from which as many as 

 thirty larvae may grow. In summer, larvae occur which are morpho- 

 logically different from the paedogenetic forms. These summer larvae 



^H^ 



Fig. 297. Diagram of reproductive organs of A, a male, and B, a female 

 honey bee, C, Longitudinal section of an ovariole of Dytiscus marginalis. 

 A and B after Comstock. ac.gl. accessory gland; be. bursa copulatrix; cgl. 

 colleterial gland; ed. ejaculatory duct; /. follicle cells; ge. germarium; ov. 

 ovary ; od. oviduct ; o. ovum ; ve.se. seminal vesicles ; so. spermatheca ; t. testis 

 (multifollicular); vd. vas deferens; v. vagina. 



pupate and the small midge-like flies which emerge lay four or five 

 large eggs; from these a further series of paedogenetic larvae arises. 



Among a few of the parasitic Hymenoptera, e.g. some Chalcididae, 

 the phenomenon oi polyembryony has been observed. This consists in 

 the development of more than one embryo from a single egg. In 

 Copidosoma gelechiae, which parasitizes a caterpillar living on the 

 goldenrod Solidago, a hundred or more embryos may result from the 

 deposition of a single egg. 



Organs of reproduction (Fig. 297). In the male the testes are usually 

 small paired organs lying more or less freely in the body cavity. The 



