o] 
MUSEUM OF COMPARATIVE ZOOLOGY. 9 
words: “Wenn die zuerst vorhandene hyaline Schicht eine gewisse 
Dicke (Figg. 60 und 61) erreicht hat, wird dieselbe vom Hornblatt ab- 
gedrängt durch eine zweite an dieses sich anbildende hyaline Schicht ; 
in das zwischen beiden Schichten entstehende Interstitium dringt von 
der Peripherie her eine einzellige Lage der spindelförmigen Kopfplatten- 
elemente, die sich vorher schon in einen spitzen Winkel gegen das 
Hornblatt am Rand der Corneaanlage gestellt hatten, ein (Fig. 62); 
sobald dieselben von allen Seiten her im Pol der Cornea zusammen- 
treffen, ist die erste hyaline Schicht von der unterdess zu der gleichen 
Dicke entwiekelten zweiten vollständig gesondert. Ebenso wie die erste 
durch die zweite, wird dann die zweite durch eine dritte neu sich bil- 
dende Schicht vom Hornblatt und darauf durch eine zweite einwandernde 
Lage von Kopfplattenelementen von der dritten Schicht isolirt ; diese 
wieder vom Hornblatt durch eine vierte neue Schicht und von letzterer 
durch eine dritte Zellenlage u. s. f.” It would thus appear that a very 
intimate connection is brought about between the ectoderm itself, the 
relatively large portion of the substantia propria derived from it, and 
the mesodermal elements of the cornea; and it should be especially 
noticed that this process goes on at a comparatively late stage of devel- 
opment, — viz. at a time when the retinal layers are being differentiated, 
and after the pigmented portions of the eye are well formed ; in short, at a 
stage only a very little earlier than that at which development is arrested 
in the eye of Typhlogobius. If such a process had ever taken place 
here, it seems almost certain that we should see some indications of it 
in such a stage as is shown in Figure 17 (Plate TIL). But, on the con- 
trary, what we do find is no connection between the epithelium over the 
eye and the immediately underlying tissue, or at least almost none, aud 
no indication of a hyaline layer on the inner surface of the epithelium. 
While, on the other hand, in older specimens (Plate IT. Fig. 6) the epi- 
dermis and the sub-epidermal tissue are in close connection, there being 
no interruptions or spaces at all, and we have here a well defined nearly 
structureless layer closely adherent to the epidermis. 
There is considerable individual variation in the size of the eye. In 
three specimens, 50 mm., 60 mm., and 63 mm. long, the diameters, meas- 
ured parallel to the long axis of the head, were respectively 0.44 mm., 
0.46 mm., and 0.47 mm. ; the diameters transverse to the long axis of the 
head in the last two of these were, respectively, 0.39 mm. and 0.47 mm. 
In another specimen 63 mm. long, the diameter transverse to the head 
was 0.372 mm. ; the diameter parallel to the long axis of the head was 
not measured in this specimen. This last measurement was made on the 
