114 On the Agamic Reproduction of a Species of Chironomus. 



Melnikow. The anal orifice is now bounded by four ele- 

 vations, which subsequently become developed into the finger- 

 like processes. The posterior pair of legs is formed by a 

 furrow, which divides the last ventral segment from beneath 

 into two elevations. Three claws appear upon the two pairs 

 of feet. At the same period the larval eyes and eleven con- 

 secutive ganglia are to be seen, occupying the lower space of 

 the ventral cavity. The yelk-sac has now become immersed, 

 and no longer appears as a separate structure ; its walls have 

 become considerably thicker. 



Lastly, the antennae and then the palpi become segmented. 

 The body of the embryo becomes much elongated ; and as it 

 lies in the envelope of the ovum, it draws this out, so that the 

 ovum now measures 0*27 millim. ; the envelope, however, is 

 still so strong that it bears this pressure ; and thus the gradu- 

 ally elongating larva is compelled at first to lie in irregular 

 folds, and then to twist itself into a spiral of 2^ turns. Even 

 at the commencement of this process, movements of the larva 

 are perceptible ; but when the larva has rolled itself up, the 

 contractions become very lively. It also now works with its 

 fore feet and mandibles, which are now perfectly developed 

 and have become brown. Contractions are also observable in 

 the walls of the stomach. 



The ovum now bursts ; and the larva, which is 0*47 millim. 

 in length, creeps about in the cavity of the homogeneous cord 

 until, in the course of a few hours, it breaks through this 

 membrane also. 



The whole process of development, from the deposition of 

 the ovum to the exclusion of the larva, lasts, in spring, from 

 eighty to ninety hours. 



I now conclude this short description of the embryonic 

 development of the species of Chironomus imder investigation, 

 and reserve it for some future day to describe the development 

 of the histological elements and organs, and also to discuss the 

 question of the lamellar theory of insect-development. 



EXPLANATION OF PLATE IIL 



Fig. 1. The string of ova laid by the pupa: a, homogeneous mass. 



Fig. 2. The newly hatched larva ; its stomach is still filled with the 



remains of the vitellus. 

 Fig. 3. A larva, 3 millims. in length, in which the pupa is developing, 



some of its parts being already visible, such as the tracheae, eyes, 



wings, and legs. Fig. 3 a, antenna of the same larva, strongly 



magnified. 

 Fig. 4. Ovigerous pupa ; its wings are bent downwards, and only one of 



them is to be seen. 



In figs. 2, 3, & 4, the lettering is as follows : — a, antennse ; 



