272 SALMONID^ OF BRITAIN. 



elements of deformity may be present either in tBe germ from the father* or the 

 mother, and be communicated to the offspring, occasioning hereditary deformities 

 which may extend over more than one generation.f 



Everyone who possesses even a very limited acquaintance with fish-culture, must 

 be aware that monstrosities among the young as they emerge from the egg are 

 by no means rare, and likewise that such can be hereditary as may be seen in 

 the race of gold-fish, Gyprmus auratus, bred by fish-culturists. Now and again 

 we find reference made to these monsters in the public press with surmises as to 

 their cause, and then the matter drops until another is recorded and furnishes 

 material for further discussion. The subject, however, is one that has engaged 

 the attention of some of the foremost men in science, and that from almost 

 immemorial ages, and if opinions are still divided as to the exact process of how 

 these abnormal forms arise, still very much information on this point may be 

 gleaned from the pages of scientific journals. I have, therefore, thought that it 

 might be interesting to bring together some notes on this subject which more 

 especially have a bearing on the monstrosities, and some pathological changes 

 as seen among the young Salmonidae, whether congenital, or occurring during inter- 

 ov^ian life being acquired ; or arise subsequent to that period and during extra- 

 ovarian life. These divisions must therefore he restricted to the embryo within 

 the ovum, or subsequent to its extrusion ; while the yelk-sac or alevin stage, may 

 properly be referred to the latter of these periods. 



Monsters, as a rule, succumb as soon as the alevin absorbs its yolk-sac, and 

 although it has been asserted that all the layings from certain females produce 

 monsters, I have not as yet had the opportunity of showing such an instance, but 

 have observed the contrary, e.g. all the young produced from a mother with bull- 

 dog deformity being perfect. 



The following divisions of monstrosities and deformities, as seen among fishes, 

 may be observed : (1) due to constitutional causes as from young parents, hybridi- 

 zation, &c. (2) Congenital or hereditary causes'^ as hereditary monstrosities such 

 as the various races of gold carp. (3) Acquired causes or accidental circumstances 

 as arrest of development or accidents to the embryo§ prior to hatching. 



As regards the effects of constitutional causes on the proportionate number of 

 monstrosities and malformations, such appears to be greater in hybrid fish, or 

 when bred from pure parents, but distinct species, than when the breed is kept 

 pure, or both parents are of one species. It thus seems clear that the element or 

 cause of malformation must exist at the period of, or subsequent to the fertilization 

 of the egg. As these monstrosities, &c., increase in hybrids interbred with hybrids, 

 if the parents are very young, the same results are seen (see p. 265 ante) ; and 

 the alevin may suffer from dropsy of the yelk-sac (plate XII, fig. 16), (see 

 p. 261 ante). 



* This may be seen in an excessive number of fingers, harelip, etc. 



t Dr. E. Cutler, Medical World, 1886, iv, pp. 18-20, suggested that abnormal forms of sperma- 

 tozoa are sometimes the cause of teratological conditions in the children, and stated that 

 abnormal forms of the following character have been observed in the sperm of man. Spermatozoa 

 with two or three bodies, with one body and two or three tails, with two bodies and two tails, and 

 with two bodies and three tails. The average proportion of these monstrous spermatozoa is 

 about 1 in 50,000, their movements are slower, but more vigorous than the normal forms. 



Monsters have been considered to be sometimes formed by an excess of development, one 

 foetus may be contained within another in almost every part, or a more or less developed rudi- 

 ment may adhere as a tumour to the outer surface of another body, and be even covered by the 

 integument. Some have been compared to parasitic disease formed in the interior of the body of 

 the foetus as hair or teeth, or rudiments of a second foetus internally or adherent externally. 

 Vrolik mentioned a fcetal calf being bom, the tongue being the sole developed portion, demon- 

 strating that merely a single well-defined organ may be present. 



J Gegenbaur has divided atavistic phenomena, or the reappearance of a more primitive 

 organization, or a reversion to a primary condition into : (1) Palseogenetic if present in the germ, 

 or by law of inheritance ; and (2) Neogenetic if absent in the germ. The existence of this last 

 phenomenon is denied by Mr, Bland Sutton (Proc. Zool. Society, 1886, p. 551). 



§ It would, perhaps, be useful in this class of fishes, to separate the embryo from the foetus 

 in description, but in practice such would be difiEcult, for although such might define a period 

 before and subsequent to the eyed period, but few would agree as to the precise time at which 

 such occurs, or what position the alevin would hold. 



