ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 723 



arises by the hardening of a thin layer diiferentiated as a fringe from 

 the rest of the yolk. It may appear before or after the chorion, and at 

 different stages of egg ripeness. On the growing egg it cannot be very 

 firm, and is capable of extension. 



The chorion is a cuticular secreted product of epithelial cells. In its 

 young state it is soft and plastic. The chorion of Musca in process of 

 being formed remained, on the contraction of the yolk, in part adherent 

 to the latter, in part to the epithelium, and became drawn out in threads. 

 Towards the close of its formation the chorion seems at length to become 

 hard ; it also undergoes, as the staining reactions show, some change in 

 its constitution. In its origin it is often unequal, forming first on the 

 inferior portion, and becoming subsequently extended upwards. 



The cellular-like appearance of the chorion is deceptive. As the 

 internal surface of the epithelial layer changes its form in the course of 

 chorion formation, it may be the condition of manifold structures on the 

 same chorion. Korschelt also shows that the same cells may successively 

 produce very different substances. The close association between epi- 

 thelial layer and chorion is emphasized, and numerous modifications 

 are described. 



The secretion of cuticular substance is not always confined to the 

 free surface of the epithelial cells, but sometimes occurs on their lateral 

 surfaces, and therefore between the individual cells. In this way flat or 

 filiform structures are formed which are in connection with the forming 

 chorion, and appear on the mature egg as little basket-like structures or 

 as a network. 



The pore-canals which penetrate the chorion often in great abun- 

 dance have their origin from processes of the epithelial cells. By longer 

 and stronger processes, yet essentially in the same way, arise the 

 elongated and superiorly expanded canals of the multiple micropyles. 



In a general way the origin of the chorion may be said to be the 

 same as that of the cuticle. A marked deviation from the typical 

 cuticular mode of formation of the chorion and its associated struc- 

 tures is that exhibited in the formation of the " egg-rays " (" Ei- 

 strahlen ") in Nepa, which take origin in the interior of modified epithelial 

 cells. In investigating the details of this process Korschelt has been 

 led to conclude that the nuclei exercise a direct and essential influence 

 on the secretory activity of the cell. Two cells fuse before the forma- 

 tion of the rays, but the fusion is quite complete, and the process takes 

 place not between two cells, but within a double bi-nucleate cell. This 

 mode of formation of chitin is indeed unique. 



Antennary Sensory Organs of Insects.* — Herr F. Euland points 

 out that, notwithstanding the great variations in the antennas of Insects, 

 they may, with perhaps one exception, be referred to a common funda- 

 mental type. The external apparatus is a more or less well-developed 

 chitinous hair which is supplied by a branch of an antennary nerve. 

 Free nerve- endings, such as have been described by Hauser in Calo]ptenus, 

 Tahanus, Vanessa, and others, do not really exist. 



The first function of these organs is tactile, for there can be no doubt 

 that a large number of the structures which are found on the antennas 

 have this office. Some of the hairs are stronger and are articulated at 

 their base. Necrojphorus and Geotrupes have peculiar organs of this 



* Zeitschr. f. Wiss. Zool., xlvi. (1888) pp. 602-27 (1 pi.). 



