_Heart._--The wall of the heart in Insects is of mesoblastic origin, and develops from paired rudiments derived from that peripheral part of each mesoblastic band which unites the somatic to the splanchnic layer. In this layer two lateral semi-cylindrical rudiments appear, which, as the mesoblastic bands meet on the dorsal surface of the embryo, are brought into contact and unite to form the heart (fig. 111). The heart is therefore hollow from the first, its cavity not being constricted off from the permanent perivisceral space enclosed by the mesoblast, but being a vestige of the primitive embryonic blastocœl, which is bounded by the epiblast, as well as by the two other embryonic layers. Such a mode of the development of the heart was observed by Bütschli in the Bee, and by Korotneff in the Mole Cricket. I am convinced, from my own observations, that the heart of the Cockroach originates in this way, though it is to be observed that, in consequence of Patten’s results,[183] the question requires further investigation. According to Patten the mesoblastic layers of the embryo pulsate rhythmically long before the formation of the heart. Patten also states that the blood-corpuscles are partially derived from the wall of the heart. [183] Loc. cit. [Illustration: Fig. 114.--Young Ovary of _B. germanica_. (Oc. 2, Ob. DD, Zeiss.)] [Illustration: Fig. 115.--Young Testis of _B. germanica_. (Oc. 2, Ob. DD, Zeiss.)] [Illustration: Figs. 116, 117, 118.--Three stages of development of tegumentary portion of Male Sexual Organs of _P. orientalis_. (Oc. 1, Ob. BB, Zeiss.) _VD_, vas deferens; _VS_, vesicula seminalis; _D_, ductus ejaculatorius; _P_, _p_, penis and its lateral appendages.]