CURRENT LITERATURE. 121 



Erlanger, R. v.— II. Ueber einige abnorme Erscheinungen in der Entwicklung 



der Cassidaria echinophora. Zool.Anz., 1893, pp. 1-6, 3 figures. 



The author finds that in Cassidaria echinophora only a very small percentage 

 of the deposited ova develop normally and arrive at the veliger condition. The 

 majority undergo irregular segmentation, and ultimately serve as food for the 

 normal embryos, or perhaps occasionally develop into dwarf-embryos. Out of 

 some 300 ova laid in each capsule, the number of normal embryos and larvre is 

 only from 4 to 12 ; and of diminutive abnormal embryos from 2 to 4. The 

 occurrence of this large proportion of malformations in the development of 

 Cassidaria is attributed by Erlanger, not to the possible failure of fertilisation, but 

 to the overcrowding of ova in the egg-capsules. 



Erlanger, R. v. — Bemerkungen zur Embryologie der Gastropodon. — I. Ueber 

 die sogenannten Umieren der Gastropoden. Biol. Centr. , 1893, xiii., i., 

 PP- 7-13- 



Erlanger summarises our knowledge of the provisional kidneys ( Urnieren) of 

 larval Mollusca. They may be either entirely ectodermal (marine Prosobranchs), 

 entirely mesodermal (Opisthobranchs), or composed of both mesodermal and 

 ectodermal elements (freshwater Prosobranchs, Pulmonates, Lamellibranchs). 

 He regards them all as homologous organs, bearing somewhat the same relations 

 to the segmentation cavity as do the permanent nephridia to the coelom. They 

 are homologous with the excretory organs of Rotifers ; and their co-existence with 

 permanent nephridia is by no means to be regarded as evidence of incipient 

 metamerism. 



Grobben, C. — Beitriige zur Kenntniss des Baues von Cuspidaria [Necera) 

 cuspidata, Olivi, nebst Betrachtungen iiber das System d. Lamelli- 

 branchiaten. Arb. Zool. Inst. Wien, 1892, x. ii., pp. 1-46, 4 pits. 



Prof. Grobben gives an admirable account of the anatomy of Cuspidaria 

 cuspidata, supplementary to, and in one or two details correcting the previous 

 observations of Pelseneer and Dall upon species of the same interesting genus. 

 In the main, however, Pelseneer's lucid interpretation of the structure of 

 Cuspidaria is confirmed. The characteristic "branchial septum" is here 

 perforated by five pairs of slits, provided with valves on their dorsal margins, as 

 described by Pelseneer. Its surface is formed by a low pavement epithelium 

 covered by a cuticular coating. Cilia are absent except in the immediate region 

 of the branchial slits. The septal muscles are composed of long, flattened, 

 unicellular fibres, which, unlike those of the other muscles, are transversely 

 striated. Grobben agrees with Pelseneer in homologising the septum with the 

 right and left lamella; of the typical bilamellate gill plumes, the outer lamella of 

 each side having degenerated, and the gill-axis being represented by the lateral 

 union of septum and mantle. The fused lamella; have lost, however, both 

 branchial structure and respiratory function ; and have become converted into an 

 accessory muscular arrangement for producing a respiratory current. The 

 transverse striation of the septal muscles indicates a power of rapid contraction. 

 By alternate contraction and relaxation, the septum probably acts like the piston 

 of a suction-pump, water entering through the branchial siphon, passing into the 

 upper chamber through the valvular slits, and out again through the exhalent 

 siphon. 



The nephridia consist each of a dorsal and a ventral limb connected 

 posteriorly, but their structure is somewhat peculiar. 



The former is a broad, flat, lobulated and glandular sac, opening by a small 

 aperture in its floor anteriorly into the mantle-cavity ; the two nephridial sacs are 

 anteriorly in open communication with each other through a short transverse 

 connecting duct. The ventral limb of each nephridium is a narrow non-glandular 

 tube opening in front into the pericardium by a ciliated funnel ; the nephro- 

 pericardial tube lies buried in the floor of the glandular sac and seems to have 

 been overlooked by Pelseneer in C. rostra/a. 



