ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 739 
gathers, while at its apices some of the pseudosomes coalesce to build up 
the colossal centrosomes. Though the author speaks (for the first time) 
of pseudosomes and dictyosomes, he points out that there is no genetic 
connection between them and centrosomes ; “ my sole reason for using 
the two new terms is their successional appearance.” 
While bringing into prominence the existence in BrancTiipus of a 
veritable “ Schaumplasma,” the author urges that he has no predis- 
position to utilize Butschli’s conception of such structure as a funda- 
mental interpretation of some of the phenomena of karyokinesis ; at the 
same time, the observation that a foam structure is intimately bound 
up with the phenomena of karyokinesis (even in a single type) must 
materially enhance the value of Butschli’s hypothesis that it is sufficient 
to account for the amoeboid activities of protoplasm. 
The author’s study of the development of the generative elements 
shows that in Branchipus the general law as to the similarity of the male 
and female cells is borne out, and that their specific peculiarities are phy- 
siological in origin and have no morphological significance. Secondly, 
the derivates of the primitive genital cells are of two kinds — one trans- 
formed directly into the reproductive elements, the other into the egg- 
case or into the fluid in which the spermatozoa are suspended ; in one 
case there is karyokinesis, in the other akinesis. Thirdly, the divisional 
phenomena of these cells are intimately related to a protoplasmic struc- 
ture, which may be called “ Schaumplasma,” and one of the initial 
physical impulses towards metamorphosis is a fusion of some of the 
intra-nuclear globules ; a considerable portion of the complicated karyo- 
kinetic figures appears to be the logical as well as the actual consequence 
of the continuance of this process. 
In Apus the divisional phenomenon exhibits a remarkable change, 
for the cells of the gonad are all alike, and can function both in slime 
and egg formation as opportunity arises. The difference is perhaps due 
to the fact that, in sexually produced species, the nuclei intended for 
fusion must, so to speak, balance one another ; any infringement of the 
rule of karyokinesis would lead to such wide abnormalities that it would 
be quickly eradicated. On the other hand, a parthenogetic or herma- 
phrodite species may please itself as to the manner in which it evolves 
its reproductive elements, so long as these contain the premises necessary 
to the proper development of the individual. 
Larval Forms of Trilobites.* — Mr. C. E. Beecher suggests the 
following classification of the stages of development of these difficult 
Cephalon predominating, other parts not sepa- 
rated from it. E. g. earliest known stage of 
Sao, Btychoparia , and Acidaspis. 
Cephalon distinct; thorax nil ; pygidium dis- 
tinct. E. g. second stage of Sao et al ., and 
Barrande’s larvae of Agnostus and Trinucleus. 
Cephalon, thorax and pygidium distinct and 
complete. Growth incomplete. 
Ephebic All parts complete, and full size attained. 
* Amer. Journ. Sci., xlvi. (1893) pp. 142-7 (l pi.). 
organisms : — 
Nauplius ? 
Phylembryonic 
Nepionic (as many 
stages as normal 
thoracic segments) 
