274 Sir John Lubbock’s Address. 
broods, differing in form, structure and habits; that in one of 
them males are entirely wanting, and that the reproduction is 
effected by fission, or by buds, which, however, are in some 
cases structurally indistinguishable from eggs. Steenstrup’s 
genera. 
Thus an insect known as Neuroterus lenticularis, of which 
females only occur, produces the familiar oak-spangles so com- 
mon on the under sides of oak leaves, from which emerge, not 
Neuroterus lenticularis, but an insect hitherto considered as a 
distinct species, belonging even to a different genus, Spathegaster 
baccarum. In Spathegaster both sexes occur; they produce 
aplera, which again gives rise to the common oak-apple. 
t might seem that such enquiries as these could hardly have 
any practical bearing. Yet it is not improbable that they may 
ead to very important results. For instance, it would 4 ga 
that the fluke which produces the rot in sheep, passes one p 
of its existence in the black slug, and we are not without hopes 
that the researches, in which our lamented friend Professor 
Rolleston was engaged at the time of his death, which we all 
so much deplore, will lead, if not to the extirpation, at any 
rate to the diminution, of a pest from which our farmers have 
so grievously suffered. It was in the year 1839 that Schwann 
and Schleiden demonstrated the intimate relation in which anl- 
mals and plants stand to each other, by showing the identity 
of the laws of development of the elementary parts in the two 
kingdoms of organic nature. Analogies indeed had been 
previously pointed out, the presence of cellular tissue in cer- 
tain parts of animals was known, but Caspar F. Wolff's bril- 
liant. memoir had been nearly forgotten ; and the tendency of 
microscopical investigation had rather been to encourage the 
belief that no real similarity existed; that the cellular tissue of 
animals was essentially different from that of plants. This ha 
arisen chiefly, perhaps, because fully formed tissues were com: 
red, and ‘it was mainly the study of the growth of cells 
