66 Dr. Burnett on the Development of Viviparous Aphides. 
When, in spiders, the serous fold of the germinating tissue has 
extended so as to cover two-thirds of the developing form, leav- 
ing the vitelline mass on the dorsal surface near one of the poles, 
the whole embryo quite resembles that of a developing Aphis 
just before the arches of the segments close up on the back. 
With this view of the relative parts of the germ, the following 
would be the details of the development of the different systems, 
and in the noticing of which I shall follow Kdlliker.* 
The germinating tissue consists of two parts; a serous and 
mucous fold. 
- The abdominal plates arise from the serous fold, sprout out 
towards the vitelloid mass, pass over it and unite on the dorsa 
surface of the future animal; on the opposite side are formed 
plates which do not unite, but are formed into the hind legs. 
e wings are the lateral limbs. 
4. The first traces of the abdominal column appear in the 
chain of abdominal muscles, situated between the nerves and the 
intestinal canal. 
the germ at the time when the first traces of development were 
seen. From this it is evident that, even admitting that these germ- 
masses are true eggs, the conditions of development are quite differ- 
ent from those of the truly viviparous animals; such as for in- 
stance in Musca, Anthomyia, Sarcophaga, Tachina, Dexia, Mil 
togramma, and others among Dipterous insects ;} or in the vivip@ 
* Kélliker, Observationes de prima Insectorum genesi adjecta articulatorum evo 
oh cum Vertebratorum comparatione. Diss. Taiae Boe Alb, Kolliker. Turi, 
A work replete with facts interesting estions. 
+ See Siebotd in Frorieps ia Notiz, iii, “3oT and in Wiegmann’s Arch. 1838, i, 
p- 197.—also his Observat. quaed! Entom., ~ p- 18. 
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