ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 443 



is largely formed from the dorsal vessel, gives off a branch which 

 extends along the oesophagus to the pharynx, irrigates the organs of 

 unknown function which are placed at the base of the gullet, and 

 passes into the ventral vessel ; the subneural vessel into which it 

 passes in Lumhriciis being wanting in the marine worm. 



The author suggests that the two separate subintestinal vessels 

 which are found in Arenicola may represent the primitive condition 

 of the single ventral vessel of the earthworm, in which case the 

 ventral of the former becomes the homologue of the subneural of 

 Lumhricus, and the homology between the " hearts " becomes more 

 complete. Other differences are due to the presence of gills in the 

 marine forms, the essential points in the disposition of the vessels 

 appear to be the same for both. 



Germ-layers of Clepsine.* — Dr. C. 0. Whitman, after noticing 

 briefly the various contributions to the embryology of the Hirudinea 

 which have appeared since his first paper (1878) on the embryology 

 of Clepsine, gives an account of some organs on which he has been 

 able to make more satisfactory observations. 



He finds now that of the eight rows of " neuroblasts " only tlie 

 two median give rise to the nerve-chain ; the outer row of either side 

 probably give rise to muscular elements, while the two intermediate 

 form the nephridia. The ganglionic-chain developes from before 

 backwards ; the nerve-collar and the supra-oesophageal ganglia are 

 certainly formed from cells that lie beneath the epidermis, and not 

 from a thickening of the epidermis itself. 



The epithelium of the archenteron arises from free nuclei belong- 

 ing to the three large blastomeres, and those which line the oesophagus 

 are the first to appear ; some of their products give rise to the salivary 

 glands. The sense-organ of the lip appears as bulb-like thickenings 

 of the epidermis. Larval gland-cells formed from epidermal thick- 

 enings (and apparently confused by Nusbaum with the originating 

 nervous system) have the function of fixing the young to their mother, 

 before either sucker is sufficiently well developed to do this. 



Genital System of Pontobdella.t — M. G. Dutilleul gives a descrip- 

 tion of the genital apparatus of Pontobdella muricata. The male pore 

 is placed on the ventral mid-line between the second and third rings 

 of the clitellum : the female pore between the fourth and fifth rings. 

 On each side are six testes connected with a longitudinal vas deferens, 

 which anteriorly opens into a seminal vesicle : this is twisted like a 

 corkscrew, and has muscular walls. From this vesicle a curved duct, 

 with thick muscular walls and glandular epithelium, leads into an 

 ovoid " spermatophoral pouch," which is lined by unicellular glands 

 placed radially to the lumen. From this pouch a short duct passes 

 medially to meet its fellow of the opposite side, and the common duct 

 thus formed opens to the exterior. The female system consists on 

 each side of a " tubular ovary with a delicate muscular wall " ; the 

 lining of which gives rise to ova and to nutritive cells. The ovary 



* Zool. Anzeig., ix. (1886) pp. 171-G. 



f Comptcs Rcndus, cii. (188G) pp. 559-G2. 



2 G 2 



