208 SUMMARY OF CURRENT RESEARCHES RELATING TO 



large cylindrical cells, which contain in their inner halves a round 

 nucleus, and a quantity of dark pigment ; the pigment-cells are in their 

 turn covered by a layer of columnar cells ; the latter layer appears to be 

 a modified portion of tho ectodermal layer of the inner mantle. Dr. 

 Dolloy supposes that the eye of Salpa is compound. The ciliated sac 

 consists of a simple tube closed at the end nearest the ganglion, against 

 which it rests, and opening at the other end into the branchial sac ; its 

 walls are made up of short, thick, columnar cells carrying heavy cilia. 



£. Polyzoa. 



Reproductive Organs of Alcyonidium gelatinosum.* — Prof. W. A. 

 Hcrdman has had his attention directed to a colony of Alcyonidium 

 gelatinosum, which was not, as is usual, homogeneous in colour and semi- 

 translucent, but had a blotched appeai'ance, due to the presence of a 

 number of small rounded spots of an opaque greyish-white or pale 

 yellow colour. These spots were found to be cavities which were filled 

 with fully developed active spermatozoa ; on further examination, some 

 of the polypides of the colony were found to contain a few young ova. 

 Prof. Herdman thinks that A. gelatinosum, like many of the compound 

 Ascidians, is an hermaphrodite in which the reproductive systems arrive 

 at maturity at different times in the life-history, but, whereas these are 

 proterogynous, Alcyonidium appears to be proterandrous. If the polypides 

 are unisexual, then this proterandry applies only to the colony, but it is 

 possible that each polypide may be a proterandrous hermaphrodite. 

 Both ova and spermatozoa occur in ordinary polypides, and not, as in 

 A. my till, in goncecia, or cells which contain no polypides. 



Anatomy of Pedicellina.| — Dr. A. Foettinger has detected on the 

 coasts of Belgium a third species of Pedicellina, which he calls P. benedeni; 

 it is characterized externally by a pedicle formed of numerous seg- 

 ments, recalling that of Urnatella gracilis Leidy, and by the rosy colour 

 of its tentacles. In its anatomical characters it agrees closely with 

 P. echinata and P. belgica ; simple or multiple bands may appear on 

 the joints of the pedicle. In all three species the segmental organs are 

 formed of two tubes which terminate at their central extremities in a 

 cell provided with a long vibratile filament ; the two tubes unite to open 

 by a single orifice which is placed at the level of the intertentacular 

 space ; they are formed of a small number of cells, and their cavities are 

 intracellular. All the forms examined were found not only to have the 

 sexes separate, but individuals of one sex formed distinct colonies. The 

 male organs consist of two testicles, which pour their secretion into a 

 seminal vesicle, from which arises a long excretory duct which opens 

 near the external orifice of the segmental canals. The female apparatus 

 consists of two ovaries, in the interior of which short oviducts arise ; 

 these unite into a common canal which ends on the floor of the incu- 

 batory chamber, not far from the anterior wall of the intestine. Glandular 

 cells are connected with the common canal and oviducts, and their con- 

 tents are probably used to form the egg-shell. The oviducal apparatus 

 not only serves for the extrusion of ripe ova, but also for the introduc- 

 tion of sjjermatozoa ; these elements are, indeed, found in the ovaries 

 themselves. 



The central nervous system is represented by a brain more or less 



* Nature, xxxvii. (1887) p. 213. f Arch, de Biol., vii. (1887) pp. 299-329 (1 pi.). 



