THE OOTHECiE OF BLATTID^. 288 



flattened base, enlarged x 20, and the micropyle enlarged x 250. 

 The irregular stopping of the ribs of the ovum and the somewhat ill- 

 defined micropyle, are very apparent in the latter. 



The Oothecae of Blattidae. 



By the late R. SHELFOIJD, M.A., F.E.S. 

 Edited by MALCOLM BURR, D.Sc, F.L.S., F.E.S. 



The egg-capsule or ootheca of the common pest of our kitchens 

 Blatta orientalis, is a familiar enough object, which requires no detailed 

 description here. Enough to say that it is composed of hard, brown 

 chitin, and in cross-section is rather pear-shaped, the thin end of the 

 section corresponding to the upper edge of the capsule. The upper 

 edge is marked by a notched crest and the crest itself shows the line of 

 dehiscence of the ootheca, this line extending about half-way down 

 the two ends of the capsule. The notches in the sutural crest are said 

 to indicate the number of embryos contained in the ootheca, but this 

 is not really true. The embryos lie head uppermost in a double row, 

 and their position and number is shown by grooves and bulgings of 

 the sides of the capsule, beneath the sutural crest. This is clearly 

 shown in the ootheca of Periplaneta americana, which is closely 

 similar to that of Blatta orientalia : in this specimen the notches 

 number thirteen, which would indicate twenty-six embryos, whereas 

 really the number of embryos is sixteen, there being eight on each 

 side of the ootheca, as shown by the slight excrescences below the 

 sutural crest. The lips of the suture are not soldered together in 

 any way, but remain closely appressed by virtue of the elasticity of 

 the chitinous walls, whilst the sculpturing and puckaring of the 

 crest doubtless play a sort of interlocking action. 



It has been stated that the young larvte escape from the capsule 

 by exuding a fluid which dissolves the material soldering together the 

 lips of the suture. This is very doubtful ; the young larvre are 

 provided with a pair of frontal vesicles which, by means of an altera- 

 tion of blood pressure, can be enormously dilated, thus rupturing any 

 covering, membrane, or egg-case. This method of escape from egg or 

 eggcase is practically universal in the insect kingdom, though the 

 position of the vesicle or vesicles varies ; in the cockroach the so-called 

 ocelli mark the position of these vesicles in the young larvfe. 



Very similar to the Blattine type is the little ootheca, which 

 belongs to an unknown Ceylon species, probably of the sub- 

 family Pseudomopinae : it is attached to the upper surface of a leaf 

 and the actual specimen, which is white mottled with brown, looks 

 singularly like a drop of bird's excrement. Quite different is the 

 really elegant egg-capsule of J\Le;/alnhlatta iiijipes, one of the Nycti- 

 borinae, a subfamily confined entirely to the New World. The sutural 

 crest is toothed and the sides of the capsule are beautifully striated ; 

 the number of contained eggs appears to be forty, judging by the 

 grooving of the sides. The capsule is much flattened from side to 

 side and is carried with the suture directed to one side, thus dift'ering 

 markedly from the Blattine position. The very similar ootheca of 

 Paratropes bilunata which 1 found in the British Museum collection 

 confirmed an opinion previously formed, r/c, that this genus should 

 be removed from the Kpilamprinae and placed in the Nyctihorinae. 



