23 



ILLINOIS BIOLOGICAL MONOGRAPHS [316 



denied by Linstow, since it consists of a much depressed lateral wing, situated 

 close to the ventral musculature (Fig. 78) and a more median enlarged portion 

 which functions as the isthmus in that the oviduct arises from it. This isth- 

 mus-like region is not in the median line but about 0.25mm. from it, the whole 

 organ altematmg irregularly from right to left, constantly opposing the cirrus- 

 sac on the other side. It varies from 0.55 to 0.64 mm. in width and has a 

 length laterally of 0.12mm. Its imusual situation is evidently due to the 

 closely crowded condition of the reproductive organs and the pressure exerted 

 by the large uterus in the median Hne. Whereas the wing has a maximum 

 dorsoventral diameter of about 60/i, the isthmus is about 95m in depth and 

 roughly ellipsoidal in shape, protruding in sections from the dorsal region of the 

 junction of the wing (Fig. 78). Ova from the isthmus were found to be oval 

 to spherical in shape and from 12 to 15m in diameter (13 to 16m, Linstow). The 

 oocapt is directed horizontally away from the side of the isthmus and from the 

 median line. Its diameter is from 18 to 20m,— with which compare the dimen- 

 sions of 88 by 66m given by Linstow. The oviduct has a diameter of from 15 

 to 20m. Taking a general dorsal course, after being joined by the spermiduct, 

 it soon receives the common vitelline duct (Fig. 98) which has only a limited 

 enlargement from a previous diameter of 10 to 20 to 30m in the form of a 

 vitelline reservoir, located close to the oviduct with a length of 40m. The 

 vitelline follicles are situated in a layer close beneath the subcuticula and un- 

 broken, excepting in the median ventral line. The individual follicles, very 

 irregular in shape, are 50 to 70m in depth and 15 to 30m in width, Linstow's 

 measurements being 65 by 47m and Kiessling's 6m in the larva. Concerning the 

 shell-gland Linstow said: "Die Schalendruse ist ein 0.088-0. 105mm. grosses 

 Organ, das dorsal von der Mitte des einen Keimstockflugels an der entsprechen- 

 den Aussenwand der Uterus liegt; die Zellen, deren kleiner Kern sich intensiv 

 farbt, sind 0.0039mm. gross. " In the sections studied by the writer it was 

 found to be a quite irregular structure, composed of greatly elongated club- 

 shaped cells with necks of different lengths which unite with the oviduct in a 

 region only about 30m in length and situated just beyond the point of reception 

 of the common vitelline duct (Fig. 98). These cells are so loosely arranged and 

 their proximal attenuated portions of such a fiUform nature that they are very 

 easily overlooked, especially since they are scattered thruout the whole of the 

 dorsoventral diameter of the medulla of the region and are interwoven among 

 the oviduct, the receptaculum, the vitelHne duct and the beginning of the 

 uterus. They form by no means such a compact organ as Linstow's descrip- 

 tion and figure would indicate. The distal ends of the cells are about 15 by 

 10m in size, while their nuclei are about 4m in diameter. Kiessling described 

 the shell-gland as similar to that of Sch. solidus, and as follows: "Die Schalen- 

 driise besteht aus Drlisenzellen, welche an feinen Stielchen befindUche Blaschen 

 an der Oberflache einer Halbkugel angeordnet sind imd ihre Stielchen als 

 Radien nach dem Mittelpunkte der Kugel senden. " His figures of such a 

 compact region are likewise quite different from conditions described here. 

 The uterus forms a mass of coils, 0.4 to 0.6mm. in diameter in the median 



