— 38 — 



fig. 5, the general principle of structare is in this part of 

 the eye the same, as in its other portions. The retinulae of 

 the anterior area, distinguished by their greater length, also 

 narrow gradually in the proximal direction. Most of their 

 luiclei are also arranged in the distal half of the cells, whereas 

 one nucleus, evidently the seventh, is situated in the proxi- 

 mal half. Those seventh nuclei of all the retinulae lie at one 

 general level. 



The transverse section (somewhat enlargened) through a 

 retinula (fig. 16) of the anterior area, passing at the level of 

 the section represented in fig. 13, reveals the arrangement 

 of the rhabdoiu cells already familiar to us. Only the 

 axial. lumen of the retinulae of the anterior area of the eye 

 is considerably narrower than in the retinulae of the rest of 

 the eye, so that the rhabdomeres nearly touch each other. 

 The retinal pigment is comparatively stronger developed and 

 diverges radially to all sides, sometimes reaching the neighbou- 

 ring retinulae. The latter are separated by large tracheal 

 spaces. Although the retinulae of the anterior area are lAvice 

 longer than the retinulae of the other parts of the eye, their 

 diameter is the same. 



AVe shall now make some general remarks on the plan 

 of structure of the retinulae in Diopsidae. According to 

 Dietrich's investigations made on numerous species of Di- 

 p te r a, the retinulae of the latter are distinguished by a constant 

 asymmetric construction (see fig. B. a copy from Dietrich's 

 drawing, near which, in fig. C, is represented a scheme of 

 a retinula of Diopsidae). According to Dietrich, the 

 rhabdomeres 1 — 3 are always arranged along one right line 

 and are directed toward the median body-line; the rhabdome- 

 res 3 — 5 also form a right line lying at an acute angle to 

 the first, „wahrend die Verbindungslinie von 5 und 6 der von 

 1 — 3 f)arallel lailft. Das siebente Khabdomer schiebt sich zwi- 

 schen i und 6 nach dem inneren Lumen zu vor". 



Further, Dietrich found between the 1?^ and 2?^ retinal cells 

 one more, the rudimentary eigth cell, or, an any rate, its 

 nucleus. 



I do not see any such asymmetrical structure of the reti- 

 nulae in Diopsidae. On the contrary, the retinula of Diopsi- 

 dae. (fig. C) is strictly bilateral-symmetrical. The rhabdomeres 

 1—6 are arranged in the form of a crown, and between the 



