ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
721 
When first placed, the spermatophore usually stands nearly perpen- 
dicular to the surface, and considerable force is required to detach it ; its 
mouth is completely plugged up with a peculiar secretion formed of 
elongated elliptical or spherical corpuscles ; these dissolve in water in 
the course of a few minutes. They seem to serve not only as a means 
of protecting the spermatozoa against contact with water, but also as a 
means of opening and clearing the way for the safer penetration of the 
spermatozoa, for this mass is impelled through the skin in advance of 
the spermatic elements. In the course of an hour the greater part of 
the contents of the spermatophore will be found to have escaped. What 
happens when a spermatophore is produced may be supposed to be 
somewhat of this kind : — As soon as the sperm-case is ready for the 
reception of its burden, the corpuscular secretion and the spermatic fluid 
are driven forward into it. The spermatic fluid would sweep the cor- 
puscular mass before it, and leave it in the basal portion of the sperm- 
case. The author is inclined to think that the charge is measured 
oif each time in the ejaculatory ducts, and that the contents of the 
vesiculae seminales are brought forward only to replace what has been 
ejected. 
After some interesting extracts from various memoirs in which the 
mode of impregnation is discussed, the author concludes with drawing 
attention to the sceptical attitude adopted by Dr. Hudson * towards 
Dr. Plate’s statements regarding the injection of spermatozoa through 
the body-wall. As may be supposed, Prof. Whitman is inclined to 
accept Dr. Plate’s account. 
Mollusca. 
Phylogenetic Affinities of Mollusca. f — The essay of Herr J. Thiele 
has a much wider scope than his principal title would lead us to 
suppose. The following is the conclusion at which he arrives : — The 
decentralization of the organs is the ground-plan which is exhibited in 
the organism of Ccelenterates and Polyclads. Each system of organs 
extends over the whole body. The higher Bilateria, on the other hand, 
show a more or less extensive centralization ; the enteron ceases to be 
branched, the numerous germ-glands unite ; motor ganglionic swellings 
are formed ; while the newly formed blood effects a distribution of the 
nutrient or excretory materials through the body, there are formed 
instead of water-vessels the primitively more localized nephridia ; the 
respiration of the whole surface becomes limited to special respiratory 
organs, and arterial blood is distributed through the body. 
The swimming movement, which was effected by cilia, is given up 
by the Cnidaria and Porifera, as well as by the Bilateria ; but cilia are 
retained by Sponges, Polyclads, and other Turbellaria, and by the 
Nemertinea; the cilia disappear from a large part of the body in 
Gastrotricha and Rotifers, Molluscs and Annelids, while in some groups 
they may disappear altogether. Their place is taken by the develop- 
ment of more or less strong cuticular structures, which afford the 
animals a better protection against unfavourable external influences, 
which must be of very great significance to the slow-swimming Mollusca 
* This Journal, supra, p. 6. 
t Jenaische Zeitschr. f. Naturwiss., lv. (1891) pp. 480-543. 
