ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
25 
from tlie blastopore, by an invagination of ectoderm ; in front of the 
mouth are two large clear cells which belong to the velum. The velum 
itself is distinguished by its very large cells, which show the concretions 
described by Sarasin, and are ciliated. 
Soon afterwards the foot is formed as an outgrowth of ectoderm 
behind the mouth ; the oesophagus shows signs of the invagination of 
the radular pouch. Shell- gland, cerebral plates and mesoderm have 
increased in size, and a large group of cells indicates the foundation of 
the pericardium. The primitive kidney becomes connected with the 
outer world by means of an ectodermal efferent duct. 
The anterior end becomes more marked off from the posterior, as the 
embryo increases in length ; torsion begins to be noticeable ; the kidney 
arises on the right side from a thickening of the pericardium. A little 
later signs of the mantle appear, and, at the same time, the rudiment 
of the renal efferent duct is formed. 
A lumen appears in the as yet solid pericardiac rudiment, and another 
in the kidney ; these two lumina are connected with one another by a 
narrow orifice, while the kidney opens into the pallial cavity, formed by 
the outgrowth of the edge of the mantle. The heart is formed as an 
invagination of the pericardium, becomes constricted in its middle, and 
so gives rise to an auricle and a ventricle. The ganglia arise in just 
the same way as in Paludina, that is, as separate thickenings of the 
ectoderm, which later on become connected with one another by com- 
missures and connnectives. The author has not seen the single ecto- 
dermal thickening lying in the median longitudinal axis, from which 
Sarasin derived the pedal, intestinal and visceral ganglia, and which he 
homologized with the ventral medulla of Annelids. At the end of this 
preliminary communication the author indicates the numerous points in 
it in which he is unable to agree with his predecessor in the study of 
the development of Bythinia. 
Cryptobranchiate Dorididse.* — Prof. E. Bergh sums up what is 
known of these molluscs, and endeavours to arrange the genera in more 
definite order. After giving a general diagnosis of the Dorididae, he 
defines the cryptobranchiate forms as holohepatic Nudibranchs with 
median dorsal gills which consist of a number of pinnate leaflets in an 
arc or circle, united at their base, and almost always retractile into a 
cavity, with “ perfoliate ” rhinophoria, with a pharyngeal bulb which is 
never suctorial. Prof. Bergh gives a general account of the anatomy of 
the family, and then takes a systematic survey of the genera. Although 
he emphasizes that his classification must be regarded as provisional, it 
may be of interest to cite the sub-families : — Bathydorididae, Hexa- 
branchidae, Arcliidorididae, Discodorididae, Diaululidae, Cadlinidae, Ken- 
trodorididse, Platydorididae, Chromodorididae, Miamiridae. 
Reproductive System of Tectibranchiata.f — Sig. G. Mazzarelli de- 
scribes the reproductive organs of Pleurobranchsea MecJcelii, Oscanius 
tuberculatus, 0. membranacevs, and Acera bullata, which have not been 
hitherto investigated. The peculiarities in the reproductive system of 
Acera, taken along with those of the alimentary and nervous systems, 
* Zool. Jahrb., vi. (1891) pp. 103-44. 
t Zool. Anzeig., xiv. (1891) pp. 233-43 (6 figs.). 
