406 KLIZABETH KIXNEY. 



under the direction and supervision of Prof. Caswell Grave. 

 It is with great pleasure that I take this opportunity to express 

 to Dr. Grave my sincere appreciation for his advice, criticisms, 

 and valuable suggestions. 



MATERIAL. 



The spinning-glands of the larval Hyphantria cunea, like those 

 of all lepidopteran larvae, consist of two long tubes, easily distin- 

 guishable by their glassy appearance, situated on either side of 

 the nerve cord and below the digestive tract. Each tube is a 

 cylindrical, folded body, averaging between 6 and 8 mm. in 

 length, or slightly less than the entire length of the caterpillar 

 which averages about i cm. In total mounts of a spinning-gland, 

 three arbitrary divisions may be distinguished, characterized by 

 differences in appearance, and, in section, by structure (Text- 

 Fig. D) ; the posterior, or secreting portion lying between the 

 eighth and eleventh segments and terminating blindly; the 

 middle portion or reservoir, bending posteriorly to the ninth 

 or tenth segment, then folding anteriorly to the fifth segment; 

 the anterior, or conducting portion extending straight forward 

 to the head where the two tubes converge and unite to open at 

 the apex of a median cylindrical organ, the spinneret. 



Each tube consists of a single layer of epithelial cells (Imms, 

 '25, p. 407), varying in shape and size according to position in 

 the tubule. The cells are arranged in two longitudinal rows 

 around a central lumen. The nucleus of each cell is charac- 

 teristically branched and very irregular. Externally, the gland 

 is covered by a thin membrane, the tunica propria, and internally, 

 the lumen is lined by the thicker tunica intima. 



The cells of the posterior region are relatively large and 

 irregular in form and contain a greatly branched nucleus. The 

 inner cell wall is irregular in surface contour, dm- to numerous 

 drops of secretion in passage between the cell and lumen. The 

 tunica intima is not readily distinguishable (Text-Fig. A, B). 

 The cells composing the middle region are greatly flattened with 

 .1 < onsequent elongation of the nucleus, and possess a clear 

 hyalin, inner border. The cavity of the lumen has increased in 

 diameter and is filled by secreted material (Text-Fig. C, D). 



