ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 259 



singly-pointed spicules, but it differs from it in having those of the 

 smaller form aggregated into a special superficial mass, instead of 

 remaining isolated and projecting into the spaces. With Trachya it 

 agrees in the latter point, but the large spicules are singly not doubly 

 pointed, and form a network instead of a number of aggregations. 



Just as the Baikal Lake has a genus of sponges peculiar to it, so 

 has the Caspian Sea, — the genus in this case is Metschnikowia of Grimm, 

 represented by the two species M. tuherculata and intermedia of 

 Grimm and by a Beniera flava of the same author, now referred to the 

 genus by Dybowsky. It is most nearly related to the widely distributed 

 marine genus Beniera, differing from it chiefly in the spination of its 

 doubly-pointed spicules. 



In all, the Russian empire is said to possess * thirty-five species 

 of marine and eight of fresh- water sponges, Spongilla lacustris occur- 

 ring in both categories. Of these, the Caspian Sea produces an 

 Amorphina besides the species of its endemic genus Metschnikoicia ; the 

 Black Sea possesses one Beniera, the White Sea twenty-three species, of 

 which six are allies of Beniera, and six are Calcisponges ; there are also 

 a Horny Sponge, three Eenierid forms, and a Chalinid. The Gulf of 

 Finland produces the otherwise fresh-water Spongilla lacustris. Of 

 the fresh-water regions, the fauna of Lake Baikal has been described 

 above ; the smaller neighbouring Pachabicha Lake produces a i)ecu- 

 liar Spongilla besides S. lacustris, while the only species found in the 

 six remaining examined localities are S. lacustris and Tr achy spongilla 

 erinaceus and Ephydatia (Spongilla) Jluviatilis. 



Protozoa. 



Cilia of Infusoria. t — In his recent essay on Cilia, Professor 

 T. W. Engelmann makes some brief but noteworthy references to the 

 Infusoria, Notwithstanding the very high specialization of these 

 " unicellular " organisms, he could not detect among them intra- 

 cellular fibres subtending the cilia, such as those which occur in the 

 ciliated epithelium of Lamellibranchs. Of this kind are not the mus- 

 cular striae of Stentor, alleged by Simroth to be in connection with 

 the cilia beneath which they course. This connection Engelmann 

 could not confirm. Certain it is that the ciliary motions of Stentor 

 are independent of the general contractions of its body. 



Encysted animalcules, still capable of swimming, offer very in- 

 structive appearances, because of the restrictions which their cilia 

 encounter (E, p. 527). 



The aboral tiara of Vorticellidfe which have left their stalk has a 

 peculiar structure, favourably studied in Carchesiiim polypinum. The 

 base from which this wreath arises forms a raised ring, which, when 

 well developed, is about 2 • 5 ^ broad and • 5 /a high. The substance 

 of this band, continuous with the ectoplasm, is strongly refracting, 



* This number has since been considerably added to by Czeruiavsky's 

 memoirs, in the Bull. See. Nat. Moscou, on the sponges of the Black and Caspian 

 Seas. One of the species mentioned by Dybowsky has since been shown to bu no 

 sponge. 



t See reference under " Ciliated Cells," ante, p. 22i. 



