OF CERTAIN CHALCIDIDÆ AND ICHNEUMONIDA. 91 
lopment of cæca over their whole surface, from their opening into the alimentary canal to 
their distal terminations, which, in all insects, are cæcal, and do not, in any way, anastomose 
with any other structure; as some have erroneously supposed them to do with the so-called 
adipose, or splanchnic tissue. 
Thus we find that in proportion to the more or less early development of any structure 
or organ, the function or instinct associated with that organ is more or less early evolved ; 
and that in proportion to the completeness of a tissue, such is the degree or perfection of 
each special function or instinct in the animal. 
Additional Note. 
Read February 15, 1853. 
The change of form and condition which the alimentary canal undergoes, after the para- 
site has ceased to feed (fig. 8) and is assuming its imago state (fig. 10), is as remarkable as that 
which takes place in the vegetable-feeding caterpillar, in changing to the chrysalis of the 
future butterfly or moth. The short narrow esophagus (e) becomes considerably elongated, 
and instead of terminating, as in the larva, in the third or meso-thoracic segment, it is 
extended, in the imago, through the meta-thoracie, into the abdominal region. In the 
anterior portion of the abdomen, the fifth, sixth and seventh segments, it is then dilated 
into a conical-shaped crop (f), which, by a constriction at its termination, and a reflexion 
inwards of its tissues to form the cardiac valve, is separated from the true digestive cavity, 
the stomach. This portion of the canal, the chylifie ventricle (f, f), which occupied nearly 
the whole interior of the body of the larva, is now restricted to the eighth, ninth and tenth 
segments. It is a powerful muscular structure, of a somewhat elongated oval shape, and 
the length of which is scarcely more than thrice its diameter. Around its termination are 
inserted, externally, the hepatic or Malpighian organs, from twenty to thirty in number 
(k), where, internally, by a reflexion of the tissues, is formed a second valve, the pylorus. 
The canal then becomes narrowed into what may be regarded as duodenum and ilium, or 
small intestine (g). Beyond this it is again dilated into a more muscular structure (A, i), 
the colon or rectum, which is usually filled with ejecta, and terminates at the anal valve. 
The canal in the imago, as in the larva, is formed of distinct layers or tissues, a muscular, 
a glandular, and a mucous; and is invested, externally, by a distinct, transparent, perito- 
neal membrane, which appears to be homologous with the peritoneal covering of the 
viscera in the Vertebrata, and processes, or reflexions of which, in these Invertebrata, clothe 
every internal organ, the salivary and hepatic glands, the organs of circulation and repro- 
duction, and the adipose tissue, and tracheæ; as expressly mentioned, in regard to the 
latter, in my article * INsEcTA*.' bab 
The tissues of the alimentary canal are, however, much changed in condition in the 
imago, from that in which they exist in the larva,—a change which is accompanied by 
some alteration of function in the entire organ. In the larva, in which the canal is little 
more than a capacious bag, the external or muscular tissue is imperfect, and consists of 
* Cyclopedia of Anatomy and Physiology, vol. ii. part 18, p. 965 (Oct. 1839). 
