80 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Alimentary Canal of Lamellicorn Larvae.* — Dr. P. Mingazzini 
describes the alimentary tract in the larvee of Oryctes, PhyllognatJius, 
Cetonia, Tropinota and Anomala — phytophagous Lamellicorns. The 
histology and physiology of each of the three regions of the gut are 
discussed at great length ; among the many special points worked out 
we may notice the dimorjihism of the ej^ithelial cells in the posterior 
part of the oesophagus, the disposition of the muscular libres on the 
mesenteron, the nuclear crystalloids of the midgut-epithelium, the 
chitinous structures of the proctodseum, and the nuclear degeneration in 
the e23ithelium of the hindgut-sac. 
The alimentary canal of Insects exhibits two extreme types : — one 
in which the stomodaeum is very slightly developed (as in the above 
larvae), while the proctodaeum is long and complicated ; another is seen 
in Orthoptera where the stomodaeum is greatly developed, but the proc- 
todaeum relatively reduced. In the primitive Thysanura both types ^ 
occur, the gut of Macliilis resembling that of Lamellicorns, while in 
Nicoletia or Lepisma the other type is approached. The author associates 
the extreme types of alimentary aj)paratus with the different habits of 
the members of the two orders referred to above, and finds another 
factor of variability in the degree of digestive power j)ossessed by the 
mesenteron in different insects. He also emphasizes the differentiation 
consequent on the proctodaeum acquiring a distinct absorbent function 
as in Lamellicorn larvae. 
The chitinous structures in the stomodaeum and proctodaeum are 
physiologically of three kinds : — those which serve for trituration, e. g. 
teeth and sj)ines ; those which retain the food, such as the tree-like 
structures in the hindgut of Lamellicorn larvae ; and those which are 
directive. Foremost among the peculiarities of the two regions derived 
from the ectoderm, Mingazzini notices the chitinous cuticle, which must 
be chemically as well as microscopically determined. Another character, 
which in the higher insects is only seen in the proctodaeum, is the 
folding, best seen in the rectum. Tlie author notes the possibly 
primitive hexamerous symmetry of the intestine : thus, the mesenteron 
of Lamellicorns exhibits double dorsal and double ventral muscular 
bundles, which with the two laterals make six divisions. He derives 
some support for this theory from the researches of Miall and Denny 
on the cockroach. He discusses Eisig’s comparison of the chitin in 
Caj)itellida3 with that of insects, but sought for the fibrillar structure 
which Eisig described without finding any trace of it. The chitin is 
regarded simj)ly as a cuticle with peculiar chemical j)roperties. The 
caeca of the mesenteron are portions specialized for regular secretion, 
in virtue of being out of contact with the food. The |)resence of un- 
striped muscular fibres in the tunic of the mesenteron leads the author 
to discuss the distribution of these elements, to protest against certain 
generalizations on this subject, and to note the intermediate forms 
between the striped and unstrij)ed types. It is interesting to find that 
in no region of the gut did Mingazzini discover karyokinetic division 
of the nucleus. The unique crystalloids in the degenerating nuclei of 
mid gut cells are probably waste products. 
MT. Zool. Stat. Neapel, ix (1889) pp. 1-112 (4 pis.). ] 
