50 MINOR ABNORMALITIES— ROUND-HEAD 



of the truncated skull. As regards the brain, "the four anterior ganglia are much compressed 

 from before backwards. The anterior pah' of ganglia (olfactory) have displaced the second pair, 

 and lie practically between, instead of entirely in front of, them." 



Causation. In the main, the defect seems to be a developmental one of germinal origin, 

 and not acquired through later injury. However, in the Salmouidae, apart from the instances 

 figured by Girdwoyn (81) and de Quatrefages (198), the occurrence of pug-headed embryos does 

 not seem to have been actually put on record. 



It is always possible that, as in cyclopia, the defect may at times be clue to pressure on the 

 embryo (Leonhardt) or some other factor depending on environment. Tornier (24-9) attempts to show 

 that the condition in question, as well as the other striking variations found in different goldfish races, 

 are due to interference with development through swelling up of yolk elements by undue inhibition 

 of water. This may conceivably explain the occurrence of isolated and irregular instances, but cannot 

 possibly account for the strictly hereditary qualities which the condition has been stated to exhibit. 



Knauthe (125-126) allowed breeding between a male and female Lcucaspius delineates v. Sieb. 

 which, though apparently normal, were derived from " puggy " parents, with the result that thirty 

 out of 250 in the offspring resembled their grandparents (i.e. a proportion of 12'5 °/ Q ). A second 

 brood from the same parents only gave a proportion of 8 °/ . 



Another male and female of Leucaspius, normal themselves though derived from " puggy " 

 parents, provided in the offspring the large number of fifty out of 180 which " reverted " to the 

 grandparental form. 



The same author, experimenting with a different species (Cyprinus aphya ?), obtained breeding 

 between two pairs of males and females, apparently normal and derived from apparently normal 

 parents, but having "puggy" grandparents. The result was that twenty out of a total of 210 in 

 the offspring resembled their great-grandparents. 



In the succeeding year Knauthe was able to obtain breeding between some of the seemingly 

 normal examples of the latest generation noted above. Six of the progeny out of a total of 168 

 were " puggy," that is to say, resembled their great-great-grandparents, and yet, as has been detailed 

 above, the intervening ancestors were all apparently normal. A control brood in a kindred species 

 of similar age reared under exactly the same conditions provided not a single example of " pugginess." 

 The repetition and extension of Knauthe's experiments are greatly to be desired. 



THE KOUND-HEADED CONDITION. 



The skull is more or less sharply humped upwards in the frontal region so as to present a 

 somewhat prominent brow, or forehead. The eyes are compressed antero-posteriorly, forming ovals 

 with the long axis vertical. The anterior part of the snout is not ventrally incurved, nor does the 

 lower jaw project markedly beyond the upper one. Tornier (250) seems to be the only author 

 who gives structural details of this condition, which he describes as having been observed by him 

 in a haddock, a carp, and a bleak. The basal axis of the skull is again always shortened. In the 

 bleak this axis showed a single sharp /\-shaped curve opposite the middle of the orbit. In the 

 haddock there were two sharp curves, one opposite the orbit and the other in front of that. Lastly, 

 in the carp the basal axis of the skull remained straight, but was extremely shortened in the region 

 underlying the brain-box and behind the eyes. 



The skeletal elements forming the posterior (hyomandibular-quadrate) limb of the suspensorial 

 arch are markedly reduced in size. At the same time, the bones forming the anterior limb of the arch, 

 as well as the other bones of the head in front of the orbital region, tend to be smaller than normal. 

 The mouth usually looks upwards as well as forwards, so that the condition is not unlike what is 

 commonly described as pug-headedness, e.g. in dogs. The lower jaw, however, does not project 

 freely beyond the upper one. 



Causation. The causation is probably of the same nature as that on which the pug-headed 

 condition depends. 



