282 NATURAL SCIENCE. 



JUNE, 



pairs of antennae of the Crustacea. Cholodkowsky suggests the second 

 pair, though the first pair have been regarded as post-oral by most 

 observers. The generally received view is that insect antennae, being 

 pre-oral, have nothing to do with those of crustaceans. We must also 

 consider the chelicerae of arachnids homologous with the antennae of 

 insects, if the latter are really post-oral, instead of with the mandibles, 

 as has hitherto been believed. Indeed, our comparison of arthropod 

 limbs seems to be once again uncertain, especially as small appen- 

 dages have been described by various observers between the antennae 

 and mandibles of some insect embryos. Further and more careful 

 researches on a number of types must be undertaken before this 

 fascinating subject of arthropod homology will be settled. Fascina- 

 ting, indeed, it is to see an undifferentiated limb of the far-off 

 ancestor of the race in one group changed into a jaw for seizing and 

 poisoning prey, in another into an organ of exquisite and mysterious 

 sense. 



The fate of the primitive body-cavity, or coelome, is also dis- 

 cussed by Cholodkowsky. In each segment the cavity divides into 

 three parts. The dorsal part (in some abdominal segments) contains 

 the rudiments of the genital glands;^ from its wall is formed the 

 muscular coating of the intestine. The lateral part disappears. The 

 ventral part becomes filled with the developing fat-body and loses 

 its boundaries ; it is believed to be homologous with the segmental 

 organ of Peripatus. This seems probable, and, if established, will be 

 a highly interesting result. It seems certain that the body-cavity of 

 the adult cockroach has nothing to do with the primitive coelome, 

 but is a " pseudocoel." In Sedgwick's well-known paper, in which 

 he proved this result for Peripatus (4), he suggested that the same 

 would probably be established for other Arthropods, and we now 

 have a striking confirmation of his views. 



In the cockroach and most other insects, the ventral surface of 

 the embryo where the appendages are being developed, is covered by 

 two membranes, the outer of which is known as the serous membrane 

 and the inner as the amnion. In the embryo of the ichneumon fly 

 {Mesochorus splendididiis, Grav.) Kulagin (5) states that these mem- 

 branes are not formed. In that of another ichneumon [Microgaster 

 glomeratus, L.) they are represented only by a small fold at the hinder 

 end of the body. This latter fly lays its eggs in the bodies of the 

 caterpillars of the Cabbage White Butterfly (Pieris hrassiccs, L.), and 

 hence it has a strong economic as well as scientific interest. The 

 last segment of the parasitic larva has the shape of an inflated 

 bladder, and seems to possess an excretory function. 



Observations on the life-history of another ichneumon fly 

 {Perilitus bvevicollis, Hal.) were made in Algeria by MM. Kiinckel 



1 The genital cells are believed by Cholodkowsky to be formed from yolk cells, 

 but, as stated in Natural Science for March (p. 55), this is contradicted by 

 Heymons. 



