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Part III. — Ninth Annual Beport 
but is separated from the Malpighian stratum of the ectoderm above by 
a distinct fissure, and from the neurochordal membrane below by a layer 
of pigment. From the foregoing description it will be seen that along the 
dorsum in LopJiius there is no delicate unpaired embryonic membrane, and 
when the median plate of dorsal mesoderm pushes its way upwards, and 
carries out with it a projecting ectodermic papilla, the first dorsal spine is 
formed as an isolated organ. Ryder has accurately described the main 
features of the development of the three dorsal spines of Lophius ; but it 
must be noted that there is no atrophy of any intervening fin-membrane 
such as Ryder speaks of (7, p. 1025) ; indeed, the sub-epidermal 
chamber enlarges as the spines develop (Plate XIV., conf. figs. 3 and 8), a 
phenomenon which is really the hypertrophy of the modified embryonic 
fin. By the fifteenth day after hatching the dorsal spines have acquired 
a central skeletal support and an enveloping musculature, the first spine 
forming a strong curved filament, in length about one-third that of the 
body, and traversed by an artery and vein ; the Second is shorter, and 
the third forms a short digitiform projection. The changes which these 
dorsal processes undergo, from the first to the fifteenth day, are as 
follows : — The cap of ectoderm lengthens, and its mesodermic core be- 
comes denser distally, while proximally the cells form loose strands 
(Plate XV. fig. 10). On the fifth day a central series of cells become dis- 
posed in columnar fashion, and by the ninth day are converted into 
cartilage (Plate XV. fig. 1 1 carf.). This rod of cartilage cells is enclosed in a 
delicate sheath of flattened cells, and the mesodermic cells around become 
elongated in the form of muscular fibres. A short distance before it 
emerges from the dorsum the cartilaginous rod is constricted, the 
muscular tissue becoming radially aggregated around, and where this 
converges proximally a plate of osteoid matter (2), like chitin in appear- 
ance, is developed upon each side. This chi tin-like substance, by the 
fifteenth day, clothes the cartilaginous rod, and distally forms the sole 
central tapering support (Plate XIV. fig. 8). At the stage just described 
(ninth day) we see, indeed, in cross-section of the distal portion of the 
spine (Plate XV. fig. 16), the osteoid core in process of formation. A 
structureless yellow cylinder {z) occupies the centre of a tube of pulpy 
secreting cells.* The glandular tube is ensheathed by flattened cells, 
while a considerable space surrounds them, intervening between the central 
strand and the ectoderm, and this space is occupied by a connective mesh- 
work (y). The integument consists of the usual double layer, the juicy 
mucous layer exhibiting very large glandular cells — indeed, the Malpighian 
stratum of the skin in Lophius exhibits very early a highly glandular 
character. The interesting question respecting the function of these 
enormous dorsal processes and the nature of their nervous supply cannot be 
decided without a more lengthened study ; but on the posterior side of 
the central rod in each spine a strand of cells passes up, and exhibits the 
features of a developing nervous cord (Plate XV. fig. 1 6 ne). 
When, as on the fifteenth day, the cartilaginous rudiment of the neural 
arch is formed, the central rod {cart.) has grown downward so far as to 
rest in a dorsal depression in the arch (Plate XV. fig. 12) ; but it is in- 
teresting to note that it arises distally, and only in advanced stages 
approaches and actually articulates with the vertebral column. 
Sections show, further, a large development of lymphatic tissue anterior 
to the pronephros. Such an occurrence of loose connective tissue below 
the medulla and mid-brain is a common feature in Teleostean embryos ; but 
iu Lophius its extent is so great that the eyes, which are usually in close 
* This is precisely the mode in which the so-called Teleostean clavicle arises 
(5, p. 7). 
