ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 839 



been studied by Milne-Edwards, Claparede, and Mecznikoff ; in this 

 form the ova present many difficulties to the student of the earlier 

 stages. In no Annelid does one find so considerable a development 

 of the cells of the ciliated circlet, as in Terebella ; they occupy about 

 a third of the surface of the body, and in section the thickest portion 

 of the ectoderm. When the somatic region begins to increase in size 

 the ciliary circlet loses its equatorial position and passes forwards ; an 

 anal circlet is now also to be observed, and at the anterior end there 

 is a buccal invagination, the elongated cylindrical cells of which aro 

 sharply distinguished from the other parts of the ventral ectoderm ; 

 the cephalic ganglion has not yet begun to be differentiated. In 

 many points of the succeeding history, the author finds himself able 

 to accept the very accurate account given by Milne-Edwards. 



The tube does not begin to be secreted at any very definite stage 

 in the history of the animal, and, apparently, does not play an im- 

 portant part in the life of the animal. Many young forms secrete and 

 then leave a tube, to lead a free life, and then form a fresh tube, to 

 leave it, and so on. In fact, Terebella may be said to be distinguished 

 by the " heterochronism of its development." The structure and 

 form of the rudimentary cephalic ganglion of Terebella is exactly 

 similar to that of other Annelids ; the cerebral commissures are com- 

 pletely formed at the time when the animal consists of 18 segments- 

 Here, also, the eye arises from a single cell, the proximal portion of 

 which becomes pigmented. Though true vessels are not developed 

 till very late, the animal is provided with blood, and with circulatory 

 organs, in the form of a cavity which surrounds the median portion of 

 the digestive tube. 



Pleurochseta moseleyi.* — F. E. Beddard gives an account of a 

 new genus of earthworms from Ceylon, which is about 28 inches in 

 length, and is made up of 260 segments ; the seta9 are developed in 

 all the rings of the body, but are more numerous in the post-clitellian 

 region, being there about 140 to each segment. The large intestine is 

 characterized by the extraordinary development of specialized glands. 

 No segmental organs were detected. 



The author describes the capillaries in the hypodermic layer, 

 which appeared to terminate in loops; in Pleurochceta they are 

 evident, and it is very possible that such are often developed in the 

 outer epidermic layer of worms and other animals, but have been 

 overlooked owing to their insignificant size. The glandular is sepa- 

 rated from the hypodermic layer by a band of fibrous tissue in the 

 region of the clitellum. The absence of segmental organs in Pleuro- 

 chceta is to be paralleled by their absence (according to Horst) in a 

 PericJiceta from Java, and by their slight development or absence in 

 other species of that genus. 



From the 86th to the 101st segment there are glandular bddies, in 

 all fifteen pairs, which lie on, but are separated from the dorsal wall 

 of the intestine ; each of these glands is faintly divided into lobules, 

 and is kidney-shaped ; the walls of the intestine are, in this region, 



* Trans. Roy. Soc. Edin., xxx. (1883) pp. 481-509 (.3 pis.). 



