276 CLA VPOLE. [Vou. XIV. 
lie more or less imbedded in it, and it is only by later post- 
embryonic development that the space is finally cleared and 
becomes as distinct as in the adult. 
The history and fate of the slight trace of the true coelom, 
as seen in the female embryo, has not been studied in detail 
and must remain a point for future investigation. As seen in 
Fig. 51, there is a distinct cavity in the mesodermic somite, 
although this is not so clearly marked in all the segments. In 
Fig. 58 the splanchnic layer of mesoderm forms one side of a 
spacious cavity, evidently resulting from the fusion of those 
parts of the somite cavities not cut off in the appendages. This 
space is a striking feature in animals of this sex and renders 
them immediately recognizable. It is, however, eventually 
obliterated; the beginning of this process is shown in the 
breaking of the splanchnic layer, thus allowing the germinal 
mass to leave the distinct true coelom. It is curious to find so 
much more reduction in the coelomic space in the male; it is 
as noticeably absent from the beginning as it was present in the 
female. At all times the germ band remains a solid mass; no 
space such as is shown in the female is ever seen. 
The loss of the coelomic cavity is without doubt a derived 
condition, as the ancestors of the insects probably inherited the 
space more or less completely from their annelid-like progeni- 
tors. The retention by the female of primitive characters not 
found in the male is a frequent occurrence, the latter sex being 
the more subject to modification. The female is the more 
conservative and adheres more closely to the primitive type. 
This inclusion of yolk in the reproductive organs is a point 
of great interest in the development of Anurida. It is a phe- 
nomenon not frequently observed in any forms, and, as far as 
known, without a direct parallel among the Insecta. There are 
certain forms, however, in which resemblances may be noted. 
Metschnikoff (74), in his classic account of the embryology of 
Polydesmus and Julus, double-footed myriapods, speaks of the 
peculiar position of the nutritive yolk in the body of the young 
embryos. It is present almost exclusively in the body cavity; 
very little is found in the intestine. This is a fact true also of 
the daphnids, where the yolk lies in the body cavity between a 
