500 SUMMARY OF CURRENT RESEARCHES RELATING TO 



bouring disks ; its cuticle becomes tlie facetted cornea, and its basal 

 membrane tbe posterior limiting membrane of tbe eje. Wbile the 

 neurilemma of the optic ganglion disappears, the ganglion itself 

 grows, gets spherical in form, and becomes sej)arated by a circular 

 groove from the rest of the cerebroid ganglion. The ganglionic layer 

 passes oiitside the optic ganglion, grows, and extends as a screen 

 between it and the compound eye, while at the same time it becomes 

 differentiated into its two primary layers. As the optic disk and the 

 ganglionic layer increase in extent the fibrils of the nervous tract 

 become separated from one another. As the former approach one 

 another the fibres shorten, and each becomes one of the iiost-rctinal 

 fibres. As the ganglionic layer leaves the perij)heral jDortion of the 

 optic ganglion it carries with it a set of fibres ; these are the pre- 

 ganglionic fibres, and they continue to serve as a means of connection 

 between the separated parts ; they do not arise from cells placed on 

 the surface of the grey cortical portion, but from others more deeply 

 situated. 



Before this elaborate examination of the history of the eye 

 M. Yiallanes deals with the skin, where he notes the presence of a 

 delicate structureless layer lying beneath the hypodermis of the 

 larva, which he looks upon as the homologue of the basal membrane 

 found by Haeckel in the cray-fish and by Graber in adult insects. 



In the larvfe studied by him there were observed between the skin 

 and the muscles perijiheral nervous ganglia, belonging neither to the 

 ventral chain nor to the stomatogastric system ; in the larva of Tipula 

 they are very remarkable for their regular and symmetrical distribu- 

 tion, a pair being found in each segment. In Musca, however, they 

 are arranged irregularly, while in Eristalis they are placed in the 

 nerve-plexuses from which arise the nerves which go to special sensory 

 organs in the anterior region of the body. 



The sensory nerves in the larvsB may terminate either by putting 

 themselves into relation with sensory hairs, or by coming into the 

 presence of a subhypodermic plexus, whence the prolongations appear 

 to terminate freely. 



The dorsal vessel is, from a histological point of view, comparable 

 to a capillary of a Vertebrate, but physiologically it is distinguishable 

 from it by being contractile. This contractility is due to the develop- 

 ment of muscular fibres in the protoplasm of its cells. The author's 

 studies on the involuntary muscles lead him to re-enunciate the doc- 

 trine of Eanvier that organic muscles, whether striated or not, are 

 supplied by nerves which, just before they pass into the muscles, form 

 a ganglionic plexus. 



The author believes that the fibril of the wing of an insect is the 

 homologue of the fibril of the muscle of a Vertebrate ; in Dytiscus the 

 primitive fibre has no sarcolemma, and its contractile mass is reduced 

 to a single column ; in Musca the same fibre has no sarcolemma, but 

 its contractile mass is made up of several columns ; in the Vertebrate 

 there is a sarcolemma. 



Each primitive fibre has on its surface a certain number of projec- 

 tions (cones of Doyere), and each of these is provided with a nerve- 



