MUSEUM OF COMPARATIVE ZOOLOGY. ay 
explanation of the method of its formation other than that implied in the 
allusion to Grenacher’s researches on Myriapoda. 
Carriere (’85, p. 178), basing his conclusions principally upon the ap- 
pearances presented by the ‘stemma’ in the pupa of an ant, believes that 
it is derived from the hypodermis by, — first, a lenticular thickening of 
the hypodermis produced by an elongation of the hypodermis cells ; and, 
secondly, by the rearrangement of the latter into two layers, one above 
the other, of which the outer remains in continuity with the permanent 
hypodermis and constitutes the ‘ vitreous body,” while the inner is trans- 
formed into the retina. The method by which this rearrangement is ac- 
complished is to be learned a little farther on (p. 189), where he says: 
“ According to my interpretation, therefore, the simple eye (Napfauge) 
and the compound eye (Facherauge) of the Arthropoda are organs which 
arise out of like components in a similar manner (through splitting of the 
hypodermis into two layers), but in their further development diverge 
from each other in two opposite directions.” 
While the authors just quoted agree in believing the retina to be an 
immediate derivative from the hypodermis, those cited below are at least 
so far in agreement as to hold that the retina is not developed directly 
from that layer. 
Graber’s objection to the view that the retina is derived from the 
hypodermis was based principally upon its total separation from the 
hypodermis and its derivatives (pigment-cells and “ vitreous body”) by 
means of the so-called pre-retinal septum or lamella * discovered by him. 
Combating Grenacher’s conclusions, Graber (’79, p. 66) says: If really 
the pigment-cells were directly continuous with the retinal cells, as 
Grenacher’s Fig. 31 (Vespa) makes them, then there would be an unin- 
terrupted transition from retina to hypodermis, and consequently the 
typical two-layer “stemma” could be considered as only a modification 
of the apparently one-layer eye of the Dytiscus larva. “Eine solche 
directe Verbindung der Retina,” he adds, “‘ mit den das Auge umsiumen- 
den Integumentzellen existirt aber nicht ; Hypodermis, Pigment- und 
Krystallkorperzellen einerseits und Retina anderseits bilden vielmehr je 
ein geschlossenes Ganzes fiir sich, indem sich eben zwischen beiden 
Straten unser praretinales Septum durch und durch zieht, und so vielleicht 
auch fiir die Zuldssigkeit der Grenacher’schen Theorie beziiglich des hypo- 
dermalen (wir sagen nicht ectodermatischen) Ursprungs der Arthropoden- 
Retina eine schwer zu tiberwindende Schranke bildet.” In his résumé 
of the principal results of his paper Graber (p. 88) gives as the second 
result : ‘‘ Die Retina des Stemma ist in ihrer ganzen Ausdehnung durch 
* I shall in the future refer to this structure as the “‘ pre-retinal membrane.” 
