938 SUMMARY OF CURRENT RESEARCHES RELATING TO 



infolding of its two lamellao. In the median line the colls of tho outer 

 layer biconio raised up in the form of a longitudinal ridgo, v.liich is 

 bounded latei'ally by tho continuation of the gastric folds. This ridgo 

 becomes separated from the mother~tissue and forms a connection 

 between the body-wall and tlic base of tlio bud-sac. Tho funiculus is 

 bilaminate at its point of origin ; the ingrowth of ectodermal cells gives 

 rise to tho material from which tho future statoblasts are built uj). In 

 the coursJO of growth the origin of tho funiculus becomes more and moro 

 separated from tho polypide to wliich it belongs, and we find it at last 

 at tho peripheral boundary of the colony just above the foot. Tho 

 author denies tho secondary division of the cell-aggregates which form 

 the statoblast into a cystogenous half and a formative mass, for the two 

 arise quite separately from one another. In CrisfatcUa tho former 

 arises as a blastula-like sphere, and is probably derived from a single 

 cell. 



The cells of tho formative mass gradually take on the form of 

 spindles, and at tho same time their contents wander round the yolk- 

 spheres until at last the nucleus alone remains visible. The inner 

 layer of the cystogcnous half forms the ectoderm ; the inner epithelium 

 of tho body-cavity and the muscles of the embryo arise from the cells of 

 the formative mass. All the buds are richly nourished by the yolk, 

 which remains in the closest connection with tho cells of the inner 

 epithelium, and consequently also with the cavities of the lophophore 

 which are lined by it. 



The spermatozoa of Cristatella do not develope on the funiculus, but 

 on the sipta, and generally near the upper surface. The ova, as in 

 PJumatcUa, are developed on the oral side of the cystid. In most points 

 which he notes the author is found to differ from Verworn, but ho 

 confirms that observer's statement as to the presence of an excretory 

 organ in Cristatella. 



Arthropoda. 



Eyes of Arthropods.* — Dr. W. Patten continues his account of tho 

 structure of the eye of Arthropods by a history of the development of 

 those of Aciliue. He finds that the larval o{)tic ganglion is comjiosed of 

 three segments, each of which is united with a segment of tho brain on 

 the one hand, and with a segment of the optic plate on the other. Each 

 segment of the optic plate bears a pair of eyes. The ocelli are composed 

 of four or more sensory spots or pits, each of which is sui)iDlied with a 

 separate cuticular thickening and a nerve ; in the centre of each group 

 of four sensory pits thex-e is a single large nucleus, the significance of 

 which is not yet understood. The pits of each eye finally unite to form 

 a thickened patch of ectoderm, with a median double row of gigantic 

 cells and a common cuticular thickening. The thickened ectoderm is 

 invaginatcd to form an optic vesicle, the inner walls of which form the 

 retina, while tho surrounding indifferent ectoderm forms a third layer of 

 cells over each vesicle ; in this way a typical three-layered eye is 

 produced. 



In the embryonic stages of eyes I.-IV., the retinfe of which are 

 invaginated without the formation of a cavity in the optic vesicle 

 (unless, indeed, the space between the median row of gigantic cells bo 



* Journal of Morphology, ii. (1888) pp, 97-190 (7 pis.). 



