1895. SOME NEW BOOKS. 423 



they surround the dorsal vessel. According to Spencer, they are 

 found in Megascolides, where a row of diverticula are connected with 

 the body-cavity through a special fissure. Both subintestinal vessels 

 in Lihyodrilns (Eudrilidac) possess similar sheaths, as does the supra- 

 intestinal vessel in Hcliodyilns and Hypeviodrilus. These spaces are filled 

 with lymphoid corpuscles, and therefore may represent lymphatic 

 vessels, such as the reviewer has shown to exist also in the sexual- 

 segment of Allolohophora. 



The pores by which the coelom communicates with the outer world 

 in Lumbricidae and some Enchytraeidae have till now remained proble- 

 Ujatical in function. Beddard describes very closely the excretory 

 organs of Oligochaeta, These exist, as the reviewer has shown, in 

 various shapes, according to the stage of evolution of the worm. In the 

 cleavage stage of most Lumbricidae, three colossal cells function in 

 t his manner ; the larvae of the Lumbricidae possess larval pronephridia ; 

 in the segmented embryos, on the other hand, we find embryonic 

 pronephridia. In the first segment the first pair is wanting, which in 

 the Polychaeta is known as " head-kidney." These degenerate in 

 Lumbricidffi and Rhynchelmis, but Beddard found, on the other hand, 

 that the pronephridia of the first segment of Octochcvtns mnltiporus 

 persist, and coalesce with the pronephridia of the next segment, 

 forming, in this way, the peptonephridia or salivary glands, which 

 then discharge into the cavity of the mouth. The pronephridia of 

 the next segment and their transformation into the real nephridia 

 or segmental organs, are treated of in my " Entwicklungs- 

 geschichtliche Untersuchungen." With the exception of Uncinais 

 littoralis (Bourne), nephridia are known to exist in all Oligochaeta ; 

 Beddard depicts their form after the classical researches of Benham 

 in Lumhricus, as well as the structure of those of Psammorycies. They 

 show the variations of their openings through the contractile vesicle, 

 which last is supposed to be wanting in Gordiodviliis. In other respects 

 the nephridia undergo manifold modifications, of which the change of 

 the original paired nephridia to a large number of small, tuft-like excre- 

 tory organs, which Benham has described as plectonephridia, is the 

 most remarkable. 



In the adult Oligochaeta the alimentary canal falls into the 

 following parts : the mouth and mouth-cavity, the pharynx, 

 oesophagus, and gut. The mouth-cavity of the Enchytraeidae is worth 

 remark because of the presence of two styles, which the reviewer 

 originally thought to be organs of taste, but which he has lately 

 found reason to believe serve for the digging up of fine roots. In 

 some forms special salivary glands discharge into the pharynx ; these 

 were first set down by the reviewer as organs arising from the 

 nephridia (in Enchytraeidae and Pevipatns). Moreover, the septal glands 

 of the Enchytraeidae discharge themselves into the pharynx; however, 

 these last are known even in higher Oligochaeta. The oesophagus of 

 many forms is provided with a gizzard, which usually fills one 

 segment only (in Ltimbvicus, the eighteenth) ; sometimes, however, 

 several gizzards are present — in Digaster and Dichogastey, two ; in 

 Pei'issogaster, three ; in Moniligaster, Heliodnlus, etc., three to ten. The 

 oesophagus of numerous Oligochaeta is provided with calciferous glands, 

 which may be present to the number of from one to eight pairs ; in some 

 instances, e.g., Eudrilidae, etc., they are unpaired, in which case they 

 are related to paired glands, which Alichaelsen terms " Chylus-taschen." 

 With the latter the diverticulum from the oesophagus of some 

 Enchytraeidae and Gordiodriliis is probably homologous. 



The vascular system of the Oligochaeta is accurately described. 



