4Q2 NATURAL SCIENCE. June, 



There are also exceptions to this rule even in these aquatic 

 groups. Thus the fresh-water Hydra has very few ova ; the Bryozoa 

 do not appear to us to have an over-supply ; the Mollusca, as a rule, 

 although marine and rather sluggish, do not have very numerous ova 

 or remarkably active larvae, yet their highest specialised voracious, 

 quick-moving forms, the squids and cuttle-fishes, have very active 

 larvae; the highly specialised Spatangoids, such as Hemiasier cavernosas, 

 Ag., and Aceste bellidifera, Thomp., protect their young, and must have 

 comparatively few of them ; while most fishes have numerous ova, 

 this is not the case with those that are viviparous or rear their young 

 in pouches that can only take in a limited number, or in their gills. 

 Professor Miall refers to this as tending to promote helplessness in the 

 young, and seems to consider this has a relation of cause and effect, 

 the helplessness being due to the fact that the parents are able to find 

 them food and protection. Does not this statement again assume to 

 answer a question awaiting strict investigation ? Do not parental 

 care and helplessness of the young appear simultaneously ? Can the 

 helplessness of the young of the kangaroo, for example, when trans- 

 ferred from the vagina of the female to the pouch, be due to such a 

 cause ? Obviously, it is a case of premature birth, or at any rate of 

 birth at a time when the young could not possibly take care of itself, 

 and it is difficult to imagine how this could be advantageous in the 

 early history of this group or arise out of parental care. Professor 

 Miall imagines that the sluggishness of the parent "promotes 

 activity" in the young, and that activity in the parent has the 

 opposite effect, and also, that the power of flight " favours a 

 sedentary life in the larvae, which is spared all effort in connection 

 with the dispersal of the species, and can give its undivided attention 

 to feeding." 



Professor Miall sees that this explanation does not accord with 

 the active larvae of the winged forms of the orders i.-ix., and he 

 endeavours to overcome this by the further assumption that the larvae 

 do not necessarily become degenerated until their self-helpfulness, 

 " care and responsibility," are taken away from them by parental 

 care. These statements are eminently true, but conflicting in spite of 

 this explanation, and it still remains obvious that the power of flight 

 in orders i.-ix. does not favour " a sedentary life in the larvae " any 

 more than it does among some birds and the bats, and the Mammalia 

 generally. There is connection between parental care and the 

 degeneration of larvae, and there is still more between parental care 

 and tachygenesis ; nevertheless, it is extremely difficult, if not 

 impracticable, to place either of these phenomena in the relation of 

 cause and effect, or even to take the first steps towards proving that 

 parental care antedated and might have caused tachygenesis. Tachy- 

 genesis occurs equally in animals that as a rule take no care of their 

 young, as among echinoderms and fishes, and yet the highly tachy- 

 genic young of the more specialised forms are found nestling in 



