68 MR. NEWPORT ON THE ANATOMY AND DEVELOPMENT 



retained in the digestive sac until the period of its perforation. In this way the food and 

 abode of the insects are maintained pure and uncontaminated, and the digestive apparatus 

 is completed, and the refuse of nutrition ejected only when the whole of the food has been 

 consumed. Thus we find the most perfect concordance between the internal as well as 

 external anatomy, and the functions and economy of the animal, exemplifying in every 

 particular the harmony of creation. 



I have stated that the digestive cavity is at first a closed sac. This species has enabled 

 me to demonstrate the fact, and further to illustrate the manner in which it is changed 

 from this form to that of a tube or canal. 



On dissecting this larva, I found that nearly the whole interior is occupied by the di- 

 gestive apparatus, which has the form of a bag, or rather of a Florence flask (fig. 9). Pro- 

 ceeding from the mouth and pharynx is a narrow short oesophagus (a), which suddenly en- 

 larges into the common cavity (b) : this occupies nearly the whole of the interior, and has 

 extremely thick walls, formed of large packets of granulated cell-masses, inclosed between 

 an exceedingly delicate muscular envelope on the external surface, and an equally fine, gra- 

 nulated membrane on the internal. It is divided from the oesophagus internally by a thick 

 fold of its mucous and celliform tissues, which here constitute a complete cardiac valve (c), 

 and prevent the regurgitation of the food. At the posterior, or larger end (d), it is con- 

 nected with a column of cell-masses (dd), which have partially coalesced on the exterior, 

 in the formation of a fibro-cellular envelope, and which, proceeding backwards, are united 

 with the common tegument of the body in the fourteenth, or anal segment (/). In the 

 centre of this segment, on the external surface, the skin and muscles separate at a definite 

 point in the formation of the anal outlet. When the change is about to co m mence, the 

 cell-masses that form the csecal end (g) of the cavity also separate and recede, and this 

 separation extends backwards to the fourteenth segment in the axis of the column of cells. 

 By the centrifugal expansion of these, and the consequent widening of the tube, the canal 

 is completed, and quickly becomes lined with a delicate membrane, like the interior of the 

 larger cavity. The digestive organ is enveloped in a thick layer of granulous matter, in 

 which the Malpighian vessels (h) and the organs of reproduction are developed. At its 

 anterior and inferior surface it covers two large sacs, the silk-glands (i). These are the 

 first developed organs of this class of structure, and are needed thus early for the produc- 

 tion of the silk which the larva spins before its change. 



The nymph state (fig. 11) was assumed by two of my specimens at the end of May. On 

 the 30th of that month I found that three others also had undergone their change, and that 

 the remaining ones were preparing to do so. The nymph had the usual form of the tribe, 

 and the sexes were now for the first time distinguished. The male nymph was smaller, more 

 slender, and with the apex of the body acute ; while the female was much larger than the 

 male, with a short projecting keel at the posterior of the abdomen — the ovipositor. 



The imago (fig. 12). — On the 27th of June, about four weeks after entering the nymph 

 state, one of the female specimens threw off its envelope and became perfect, and proved 

 to be a species of the genus Monodontomerm. A few days afterwards one of the males 

 appeared ; and in the course of a week, before the 3rd of July, most of my specimens had 

 become perfect. 



