ZOOLOGY AND BOTANY, MICROSCOPY, ETa 447 



yolk; both contain true protoplasm (hyaloplasm) and nutrient gra- 

 nules ; when segmentation is completed the egg has a layer of outer 

 cells, which become the ectoderm of the larva, and an internal mass 

 of granulations, in the midst of which it is difficult to distinguish the 

 cell-walls ; the origin of the mesoderm has not yet been discovered. 



The larva, which is at first globular, elongates and becomes ovoid 

 in form ; towards one extremity the ectodermic cells segment more 

 rapidly, and give rise to a cylindrical epithelium provided with long 

 vibratile cilia ; these form a collar, which surrounds the larva trans- 

 versely, and divides it into a short swollen portion, which will be the 

 head, and an elongated more delicate posterior part, which gives rise 

 to the thorax and abdomen. The cilia of the collar elongate, and 

 become very large ; the head becomes provided with some rigid points 

 which recall by their appearance the cnidocils of the Coelenterata ; 

 two eyes, formed by pigment-spots of irregular contour, appear at its 

 base, and the branchial tentacles arise as lateral lobes, which bifurcate 

 or trifurcate. The first segments to appear are those which belong 

 to the thorax of the adult ; they are provided laterally with short 

 parapodia, which carry one or two fine setee. The anterior part of 

 the digestive tube is large, and the posterior delicate and elongated : 

 all the cells of the intestine, from mouth to anus, are covered by 

 active vibratile cilia. In this condition the larva secretes a delicate 

 transparent tube, which envelopes it entirely, but which it can easily 

 leave. Development henceforward proceeds very rapidly, and all the 

 regions of the body proceed to take on the form which they have in 

 the adult ; a larva which was inclosed in mucus on the 29th of April 

 possessed on the 13th of May eight well-marked segments and a good 

 supply of cephalic tentacles ; a week later two rings had been added. 

 This species possesses the great advantage to the embryologist of being 

 one whose larvee can be continuously studied. 



' Challenger ' Gephyrea.* — The Gephyrea collected by the 

 ' Challenger ' are reported on by Prof. E. Selenka ; the forms are 

 defined as Annelids with degenerated segmentation, without external 

 jointing, parapodia, or gills. There is a closed vascular system, and 

 one to three (rarely six) pairs of segmental organs. There are seldom 

 numerous setae, and in most species none. The collection is rather 

 small, and the condition of some of the specimens has prevented their 

 being studied anatomically ; a more complete figure of the male 

 Bonellia viridis than any yet produced is given. 



As an appendix to the report, Prof. Selenka has a few notes on 

 Chsetoderma (C. militare sp. n.), the systematic position of which is 

 not, in his opinion, yet determined ; the new species differs only from 

 the North Sea species (C. nitiduluni) in the form of its spicules. 



Strongylus Axei.t — Dr. T. S. Cobbold refers to the discovery by 

 Prof. Axe, in the stomach of a donkey, of this Nematode, which is 

 remarkable for its small size, being only about 1/5 in. in length. 

 The body is filiform ; the mouth simple ; the oesophagus short. The 



* Reports of the voyage of H.M.S. ' Challenger,' xiii. (1885) 25 pp. and 4 pis. 

 t Joum. Linn. Soc. Lond., xix. (1886) pp. 259-63 (1 pi.). 



