1884.) Recent Literature. 397 
and coleopterous larve ate also capable of destroying young shad. 
Transparency is no safeguard against any of these enemies. 
' Well worthy of the attention of all naturalists are the original 
observations and categorical facts brought together by Mr. Ryder 
to prove that there is between ova, even of allied genera, con- 
siderable difference, and that at no stage is there a positive iden- 
tity. 
The mechanical construction, as it may be termed, of ova 
affects the course of their development. The Teleost ovum has 
a relatively enormous yolk, which must be included by the blas- 
toderm in order to be absorbed, and this relatively large yolk has 
much to.do with the difference observed between its development 
and that of a Marsipobranch or Amphibian. The eggs of the 
Salmonidæ have an abundance of oil drops in the vitellus, espe- 
cially just under the germinal disk. These, by their buoyancy, 
cep. the disk constantly directed upward. The cusk, the crab- 
eater, Spanish mackerel and moon-fish have eggs which arè buoy- 
almost exactly opposite to the germinal disk, and thus keeping 
it face downward—just the reverse of what occurs in the salmon- 
oids. Even after hatching, the young are at first unable to right 
themselves on account of the presence of the oil-drop. The cod 
ovum has no oil-drop, yet floats with the germinal disk down- 
wards. That of Morone americana (white perch) is adhesive and 
fixed, with a very large oil-sphere which keeps the disk on the 
lower side of the vitelline globe. The shad egg is non-adhesive, 
and heavier than water, and the germinal disk has.a constant 
tendency to arrange itself at the side of the vitellus as viewed from 
ve, though there is no oil to influence it. In Fundulus and 
Syngnathus the oil-drops appear uniformly distributed. The num- 
ber of proto-vertebrae or primary somites differs so much that 
while Tylosurus has as many as seventy-five pairs, Alosa has only 
eighteen to twenty. Our author ventures this bold remark: 
When our knowledge is more complete, we shall perhaps be 
able to distinguish the species apart by the eggs alone, just as 
botanists have used the characters presented by seeds to distin- 
oF shall or ought to hold to the doctrine that the protoplasm 
of which a man is made is different from that of which the body 
a dog or fish is composed,” ; 
Laaneti similar bricks may be formed into widely different 
kind A but it does not follow that the clay differs. same 
es or clay may enter into the grandest erection and the mean- 
a Raie two very similar buildings may be made of different 
è Something the same, we conceive, occurs with protoplasm. 
