78 ACCOUNT OF THE PHASMIDAE, WITH NOTES ON THE EGGS. 



with teeth and tubercles in various species, and these apparently afford good specific 

 characters (PI. IX, Figs. 18, 19). 



The egg. A correct account of the structure of the eggs of two or three species 

 of Phasmidae has been given by Leuckart 1 . As his account includes no reference to 

 the incomplete egg or the mode of its growth the following observations may have 

 some value. Phasmidae are insects of extreme interest ; they appear to be the 

 nearest living representatives of an Insect-fauna that was predominant in the car- 

 boniferous epoch ; they exhibit an astonishing variety of grotesque forms, looking as 

 if they were constructed of vegetable matter (so that some of them are called 

 walking-leaves, others stick-insects) and they attain a size that is much above that 

 of insects generally. They are exclusively vegetarian in diet, and are amongst the 

 most inactive of insects. The climax of their peculiarities is found in the extremely 

 perfect structure of their eggs and the resemblance of these eggs to seeds. The 

 egg of a Phasmid has not only a general resemblance in size, shape, colour and 

 external texture to a seed, but the anatomical characters of certain seeds are repro- 

 duced on the external surface, there being a hilar area, a hilar scar, and a capitulum 

 corresponding to the micropylar caruncle of such seeds as those of the Castor-oil 

 plant (Ricinus communis). The hilar area on the inner face of the capsule is, in 

 shape, like the embryo of a plant (PI. IX, Fig. 28). Moreover naturalists who have 

 examined these eggs declare that the minute structures of this curious egg-capsule 

 cannot be distinguished histologically from plant-structures. I think these resemblances, 

 in the eggs I have examined, have no bionomic importance for the species. We have 

 figured and described several of the eggs brought back by Dr Willey, and I have 

 also added descriptions of two or three other interesting eggs obtained elsewhere. 



In the examination of these eggs I have received much kind assistance from 

 Dr Willey, and I think it may be of interest to state a few points we have 

 ascertained as to their structure and the mode of their formation. I have examined 

 the ovaries in Eurycantha horrida and in Anchiale confusa from specimens of these 

 species brought back by Dr Willey in spirit and in a specimen of Hermarchus 

 pytltonivs brought from Rotuma by Mr J. Stanley Gardiner. As these ovaries contain 

 eggs in various stages of development it is possible to form an idea as to their 

 mode of growth that may to some extent approximate to what actually occurs. 



The capsule proper of the egg, or outer shell, is called chorion by Leuckart 

 (who distinguishes an exochorion and an inner layer or endochorion) ; inside the 

 chorion there is an inner membrane, the vitelline membrane or oolemn. The other 

 important parts are the operculum, capitulum and micropylar area. All the parts 

 of the egg are to the least detail formed in the ovarian tube. The operculum 

 is present as a distinct part from a very early date, and so is the capitulum in 

 those eggs in which it exists. When the egg is about half-grown the future 

 exochorion forms merely a coat of quite soft matter which appears to appertain as 

 much to the ovarian tube as to the egg ; it can be removed with ease by a 

 brush, and the egg is then found to consist of a yolk surrounded by two membranes 

 .similar in thickness. Of these the outer one subsequently becomes the inner wall of 



1 In Muller's Arch. Anat. Physiol. 1855, pp. 214—220. 



