7'J4 SUMMARY OF CURRENT RESEARCHES RELATING TO 



pouch ; the branched portion of the gland of Sacculina is absent. 

 The author concludes with the reflection that his investigation of the 

 nervous system has been rendered easy, not by special address in 

 dissection, but because of the morphological knowledge which he had 

 gained from the study of Sacculina. 



Vermes. 



Differentiating Embryonic Tissues.* — Dr. C. O. Whitman finds 

 that each of the germ-bands in the developing egg of Clcpsine is 

 made up of three distinct layers; (1) an epidermal layer; (2) a 

 layer, consisting of four longitudinal rows of cells ; (3) a deeper 

 layer, next the yolk, composed of longer cells. The layer (2) is the 

 product of the four larger cells, " neuroblasts," at the posterior end 

 of each germ-band. The third layer is derived from a large " meso- 

 blast," which lies below the preceding. 



Tho author confirms his previous statement that the nerve-cord is 

 formed from the neuroblasts, but finds that only one row on each 

 side, nearest the median line, takes part in its formation. These arc 

 stained a faint brown by osmic acid. (The author's method has 

 been already given. j) The outermost row on each side gives rise to 

 muscular tissue, and the two rows between these, which arc much 

 more deeply coloured by osmic acid, dcvclope into ncphridia. The 

 author is uncertain whether these rows of cells extend into the 

 prostomium ; but the cerebral ganglia and nerve-ring are formed from 

 cells below the epidermis, and not from a thickening of epidermis. 

 There is a thickening of the epidermis overlying the four sub- 

 cesophageal ganglia, but this gives rise to glands, which serve later 

 on to attach the embryo to the parent. These gland-cells are stained 

 deeply. The epithelium of tho alimentary tract, except stomodceura 

 and proctodceum, is formed from free nuclei belonging to the three 

 large blastomeres. The alimentary tract is formed from in front 

 backwards. 



The sense-organs on the lip arise as bulb-like thickenings of the 

 epidermis ; two pairs of these are present at the time of hatching, 

 and before the eyes and segmented sense-organs appear. From their 

 symmetrical arrangement, the author thinks that these sense-organs 

 are primarily segmental. 



The Rhabditidse.J — Dr. L. Oerley has published a monograph 

 on these ncmatoid parasites in which their medical relations as well 

 as their structure and natural history are considered; greater attention 

 has been directed to these worms since 1879, when there was an 

 epidemic on board the training ship ' Cornwall ' in the Thames ; this 

 epidemic was thought to be due to ffliabditis tcrricola, but Dr. Oerley 

 shows that that ncmatoid is a monogenous form which always leads 

 a free life, and cannot exist in the digestive tract of mammals : the 

 heterogenous forms — or those which lead a hermaphrodite and 



* Amer. Natural., xix. (1SS5) pp. 1134-7. t See this Journal, <»itr, p. 15. r >. 

 % 'Die Rhabditiden und ihre ineclicinischc Bedeutung,' 8vo, Berlin, 1886, 

 84 pp. and 6 pis. 



