232 SUMMABY OF CURRENT RESEARCHES RELATING TO 



almost wholly confined to the canal proper, not passing into the 

 villi, sacs, &c. Sometimes the circular muscles are compacted into 

 a sort of membrane, while the longitudinal strands have a looser 

 course, or the reverse may occur; in Bomhus the circular muscles 

 seem to lie outermost. In most larvaj, the circular bands are less 

 strongly developed ; in the adult forms, the longitudinal. The 

 cylindrical elements of the longitudinal muscles frequently enclose 

 at intervals a cavity, in which a long nucleus lies. There is no 

 special " serous " membrane outside the muscular layer, though the 

 external bands are frequently bound together by the loose connective 

 tissue. 



The epithelial cells. — (1) The internal epithelium may present 

 a flat surface, or exhibit villi and other elevations. The crypt-like 

 glands first noted by Basch are described, and the various occurrence 

 of two distinct kinds of cells — cylindrical and mucous — in the 

 apparently homogeneous epithelium of caterpillars is specially 

 noted. (2) The secreted material inside the epithelial cells occurs 

 in three different forms, in different groups ; (a) not definitely 

 characterized either in colour or form ; (h) colourless, but of definite 

 form ; (c) with a more or less bright colour, and with definite form 

 and disjiosition within the cells. The mid-gut of the bee larva is 

 described with reference both to its histology and i)hysiology, and 

 the various changes of the epithelium are noted. Epithelial cells 

 with colourless, but definitely formed, mostly spherical secreted 

 substance, &c., are next discussed, and finally those of the third type. 

 The distribution and structure of the mvcous cells, characteristic of 

 the caterpillar mid-gut are noted, and special attention is directed 

 to the " theca " or " secretraura " which occupies so large a part of 

 the Of IT. 



Th" hair-fringe. — The author maintains firmly his previously 

 expressed opinion as to the structure of the cell-fringe, which he 

 believes to be composed of fine hairs. This he has observed not 

 only in these epithelial cells, but in the cells of the so-called liver of 

 Crustacea and MoUusca, on a Gregarine and elsewhere. Leydig has 

 also observed a similar fringe, but has interpreted it as a cuticle with 

 pores. Dr. Frenzel affirms the frequent occurrence of the fine hair- 

 fringe, and since he believes that the hairs are mobile, proposes to 

 distinguish under the general term Wimper-zellen, those with cilia 

 strictly so-called, and those possessing the hair-fringe. As to their 

 physiological import, he suggests that they serve as a protective 

 cuticle, in some cases j^hysically, to prevent hard food-particles 

 coming into direct contact with the cells ; in other cases, perhaps 

 chemically, to prevent the injurious influence of other secretions, in 

 fact to prevent self-digestion. 



The nuclei of the mid-gut epithelium. — An interesting descrip- 

 tion is given of the varied nuclear structure of the epithelial cells. 

 The typical nuclear network, described especially by Flemming, is 

 frequently exhibited ; often complicated however by the presence of 

 " iiucleolids " or • nucleolus-like bodies. The chromophilous sub- 

 stance in such nuclei takes the form of granules arranged peri- 



