276 Tue Microscope. 
system. Prof. Sollas obtained his material at Roscoff on the 
English channel, and it is noticeable that the embryos are re- 
tained in the tissues of the parent for a longer time than in the 
case of the same species in the Mediterranean. This is ac- 
counted for on the basis of natural selection. In the channel 
the tides and currents are very strong and were the young set 
free at an early age they would run a good chance of being 
swept away from favorable localities; in the Mediterranean 
no such dangers exist and it is obviously for the benefit of the 
parent to set its progeny free at the earliest moment and thus 
save the drain on the parent. Prof. Sollas indulges in some 
speculations as to the relationship of the sponges, and agrees 
with all other morphologists that the protozoan nature advocated 
by Clark and Saville-Kent is not warranted by the facts. He is 
inclined to make a third division of the animal kingdom (be- 
sides the Protozoa and Metazoa) for the reception of the 
sponges for which he coins the name Porozoa. We have great 
doubts as to the validity of this course; at all events the argu- 
ments advanced are far from conclusive. 
Symprosis.—Dr. Keller in the course of an interesting paper 
on Cotylorhiza (Ree. Z. 8., 1 p. 405,) touches upon the question 
of symbiosis. For some time past there has been a dispute 
whether certain cells in the tissues of some of the lower marine 
animals were really component parts of the organism or whether 
they were of the nature of alge, living a sort of parasitic life, 
which proved of benefit to both. Dr. Keller inclines to the 
latter view, at least in regard to the yellow cells found in 
Cotylorhiza. The subject is an extremely interesting one and 
we may recur to it again. 
ANATOMY OF INsEcts.—We would call the attention of the 
readers of THE Microscope to the valuable series of articles now 
being published in Hardwicke’s Sctence Gossip on the anatomy 
of the cockroach, by Prof. L. C. Miall and Alfred Demsey. The 
first article was published in March, and gives an account of 
the external appearance, the habits, etc. In May the external 
skeleton, mouthparts and other appendages were described. 
The alimentary canal was taken up in July, and the respiratory 
and circulatory organs in September. In the November num- 
ber the nervous system and the eyes are described. Any one 
