586 



TEXT-BOOK OF ENTOMOLOGY 



Wheeler has observed three pairs of broad-based chitinous " hatch- 

 ing spines " used by Doryphora in rupturing its embryonic enve- 

 lopes, and which are secreted by pyramidal thickenings of the 

 hypodermis (Figs. 555, 556). 



The hatching spine of Pulex cam's (Fig. 557) is a thin vertical 

 plate, like the edge of a knife, situated in the median line of the 

 head very near the posterior end, and is somewhat cultriform, the 



FIG. 555. The three 

 pairs of hatching spines 



FIG. 556. Rudiment of 

 the hatching spine : eb, being 



on the late embryo a thickening of the ectoderm 

 of "Dory phora. After (ec) in embryo Doryphora 

 Wheeler. after formation of the heart ; 



e, serosa. After Wheeler. 



mx mx 



FIG. 55T. Head of freshly hatched 

 larva of Pulex canis: eb, "hatching 

 spine; ant, autennse; md, mandible ; 

 mx, maxilla; ma>\ 2d maxilla; Ibr, 

 labrum. 



upper edge slightly hollow, and turned up a little at the anterior 

 end. Though we did not see it working, it is situated at just the 

 point on the head where it would come in contact with the egg-shell, 

 and it was evident that the larva, by moving its head back and forth, 

 would produce a slight split in the chorion and cause it to burst 

 asunder. Later on in larval life it disappears, probably at the first 

 moult. 



LITERATURE ON EMBRYOLOGY 



Koelliker, Albert. Observationes de prima insectorum genesi, etc. Turici, 



1842, pp. 29, 3 Pis. 

 Rathke, H. Zur Entwickelungsgeschichte der Maulwurfsgrille (Gryllotalpa 



vnlgaris}. (Mullet's Archiv, 1844, ii, p. 27, Figs. 1-5.) 

 Zaddach, G. Untersuchungen tiber die Entwicklung und den Bau der Glieder- 



thiere. I. Die Entwicklung des Phryganideneies. Berlin, 1854, pp. 138, 5 Taf. 

 Ueber die Entwicklung der Insekten. (Schrift. d. k. phys.-oekon. Gesell. 



Konigsberg, viii Jahrg., 1867, Sitzb., p. 16.) 

 Leuckart, Rudolph. Die Fortpflanzung und Entwicklung der Pupiparen. Nach 



Beobachtungen an Melophagus ovinus. (Abhandl. Naturf. Gesell. Halle, 



iv, pp. 1-82, 3 Taf.) Halle, 1858. 

 Huxley, T. H. On the organic reproduction and morphology of Aphis. Pt. I, 



1858 ; Pt. II, 1858. (Trans. Linn. Soc., xxii, pp. 193-219, 221-236, 5 Pis.) 



