233 



In shape they are elongated pyriform, conical, and somewhat 

 digitiform, being slightly contracted at the base. They remind one 

 of the shape of the appendages of insect-embryos just when the joints 

 are beginning to appear. The free end is conical, rounded and imper- 

 forate. They are not capable of being retracted, and appear to be per- 

 manently evaginate , since each pair along the side of the abdomen is 

 of the same general length and size , none being either wholly or in 

 part retracted. 



To examine the microscopic structure of these processes transverse 

 and longitudinal sections of the insect in the first and last larval sta- 

 ges were made, and stained, some with alum cochineal and others with 

 alcoholic cochineal. In a longitudinal section (Fig. 2) the lumen (/) 

 is seen to be a deep narrow cavity ; it is composed of a thin mucus- 

 like coagulated fluid, containing granules of varying degrees of fine- 

 ness, which take the stain readily. At the mouth of the lumen are 

 collected fine nuclei [he] which take a dark stain ; they are surrounded 

 by a slight transparent pale protoplasmic envelope , and are probably 

 blood-corpuscles 2. 



The glandular cells themselves are modifications of the cells of 

 the hypodermis. Those in the free end of the process are very much 

 elongated, and the large nucleus is situated near the outer, broader 

 end of the cell. In some of the nuclei, which are oval, indistinct 

 nucleoli are to be seen. The nucleus is densely filled with granules, 

 the chromatin, which take a deep stain. The specimens had been pre- 

 served in alcohol , for at least three years, so that the exact histologi- 

 cal structure of the nuclei could not be clearly brought out, but in the 

 general appearance of these glandular cells there is a strong and sug- 

 gestive resemblance to those of the pleuropodia of insect-embryos, 

 figured and described by Mr. W. M. Wheeler 3, though the masses 

 of chromatin are not so distinct and isolated. 



We are disposed to regard these organs as homologous with the 

 prothoracic osmateria of the larvae of Papilionidae, and the eversible 

 lateral abdominal glands of Hemileuca and Hyperchiria, the sternal 

 and dorsal eversible repugnatorial glands of various other lepidopte- 

 rous larvae ; also wich the repugnatorial prothoracic glands of certain 



2 My friend Mr. W. M. Wheeler , to whom I have shown the accompanying 

 sketch, also thinks these are blood corpuscles; and he suggests that the granular 

 matter adjoining is the blood-plasm. 



3 W. M. Wheeler, On the appendages of the first abdominal segment of 

 Embryo insects. Trans. Wisconsin Acad. Sc, Arts, etc. VIII. p. 87—140. Sept. 20. 

 1890. 



