164 SUMMARY OF CURRENT RESEARCHES RELATING TO 



are formed within the embryo, and the appearance of the vitelUne 

 reticuhim is delayed. Previous investigators have found the seat of 

 blood-formation in a mesodermic mass between the notochord and the 

 gut, and Jolly confirms this. Later on, when the mesodermic mass (the 

 intermediate mass) is dissociated, blood-cells appear singly or in little 

 groups at the expense of extra-embryonic mesoderm. This is a primitive 

 mode of development, of secondary importance in Teleosteans. It is 

 suggested thai the peripheral extra-embryonic seat of formation has 

 become incorporated in the body of the eml3ryo to form the median 

 primordium. J. A. T. 



Life-history of the Angler. — Alexander Bowman {Scient. Inves- 

 tifjations Fishery Boards Scotland, 1920, 1-42, 6 pis,, 2 charts). A study 

 of the eggs and larvae of Lophius piscafoi-ius. The eggs, after expulsion 

 from the ovary, are found floating in the sac enveloped in a ribbon- 

 shaped mass of light violet-grey mucus, many feet long. They are 

 arranged in a single irregular layer, each free in a polygonal com- 

 partment, oil-globules uppermost. The isolated egg is pelagic, large, 

 and transparent, with a,, homogeneous yellowish yolk. It is typically 

 oval in shape, with a variable number of oil-globules like burnished 

 copper or amber. The newly-spawned egg is entirely free from 

 pigment, but even before the embryo begins to assume definite form 

 dark dendritic pigment appear on the surface of the embryo and on 

 the yolk near the embryo, and this pigment spreads rapidly. The 

 embryo does not extend round the whole egg before it is ready to hatch 

 out ; the tail remains quite free from pigment. 



The newly-hatched larva, 4'5mm. long, is a striking object. It 

 floats with the yolk uppermost ; the head, being heaviest, is lowest ; 

 thus the larva in still water assumes an oblique position, with the tip 

 of the tail just touching the surface film. The yolk is still relatively 

 large, its diameter being more than half the length of the larva. The 

 body and the gut are richly pigmented. The pigment-free tail is short 

 and fleshy. The mouth is closed. 



Even the seven to eight days' old larva floats yolk uppermost, the body 

 lying obliquely to the surface film. As the pelvic fins get shunted 

 forwards till anterior to the fan-shaped pectorals, the larv* gradually 

 sink towards the bottom of the aquarium. In the summer months the 

 absorption of the yolk is completed in about fifteen days. At this stage 

 there was still no depression of the head or body, but a superficial 

 tadpole-like appearance. The mouth is now open and well formed. 

 The pelvic fins are long, simple, filamentous rays. 



A post-larval form, about 10 mm. long, with tliree well-developed 

 first dorsal rays and the beginning of the second dorsal and anal fins, 

 shows the first signs of the change which leads to the adult shape. 

 The pelvic fins develop subsidiary lobes, and their rays become very 

 long. The changes on to the time when the young fish takes to the 

 bottom are described — e.g. the changes in the form and in the relation 

 of the paired and unpaired fins, the enormous lateral expansion of the 

 head behind the eyes, the shifting of the eyes from their original 

 lateral position to the top of the head, the multiplication of seaweed-like 

 taffs of skin. 



