192 SUMMARY OF CURRENT RESEARCHES RELATING TO 



plasm and enlarged nucleus. The metakinesis is very brief, and few 

 observations of this phase were made ; except that the loops extend 

 almost over the entire cell, the process seems typical enough. The 

 regular barrel form of the separate nuclei, the daughter- asters and coils, 

 and the like, are followed out. 



7- General. 



Adelphotaxy.* — Prof. M. M. Hartog has a note on an undescribed form 

 of irritability, which he calls adelphotaxy. It may be defined as con- 

 sisting in the tendency of spontaneously mobile cells to assume definite 

 positions with regard to their fellows. In AcMya the zoospores lie in 

 the sporange before liberation closely appressed together, with their long 

 axes parallel ; on liberation, they do not separate and swim off each on 

 its own account, but remain near the mouth of the sporange. They there 

 form a hollow sphere, each zoospore rotating round its long axis before 

 encysting in its place. The only explanation of these phenomena is 

 that the zoospores are endowed with a peculiar irritability, in virtue of 

 which they tend to place themselves close together side by side, with 

 their long axes parallel. 



Though rare in the Vegetable Kingdom, two good instances occur in 

 the Chlorophytes, in Pediastrum and Hydrodictyon ; possibly the forma- 

 tion of Plasmodia is a mode of adelphotaxy. The principle appears to 

 afford a ready explanation of many cases of cellular aggregations in the 

 animal embryo, and the formation of the spermatophores of many 

 animals. 



Functions and Homologies of Contractile Vacuole in Plants and 

 Animals.f — Prof. M. M. Hartog has a preliminary note on the contractile 

 vacuole. He finds that all naked protoplasmic bodies living in fresh 

 water have at least one contractile vacuole ; the possession of this is 

 quite independent of the systematic position of the organism, and of the 

 presence of chlorophyll, The vacuole loses its contractility on the 

 formation of a strong cell-wall or cyst, and may even disappeai'. It is 

 absent from Opalina, Gregarinida, and the Eadiolaria which inhabit 

 saline liquids. "When, owing to morbid conditions, the efficiency of the 

 contractile vacuole is impaired, excessive vacuolation and diflfluence 

 ensue. Conversely, as soon as contractile vacuoles appear, the tendency 

 to excessive vacuolation and diffluence is arrested. Prof. Hartog 

 suggests that the perforation of the nephridial cells in Vermes and 

 embryonic Molluscs, and of the ej)iblastic gland-cells of Vermes and 

 Arthropods are due to persistence of the contractile vacuole, the opening 

 of which has become permanent. 



Annelidan Affinities in Ontogeny of Vertebrate Nervous System.:]: 

 — Dr. J. Beard gives an account of some observations on the develop- 

 ment of the central nervous system of a lizard. He points out that the 

 cranial and spinal ganglia do not arise as outgrowths of the central 

 nervous system, but from epiblasts outside and beyond its limits ; this 

 is just what happens with the parapodial ganglia of Annelids. Dr. Beard 

 thinks he has discovered evidence of the bilateral origin of the central 

 nervous system, for the two bands of neuro-epithelium are separated 



* Ann. and Jlag. Nat. Hist., iii. (1889) pp. 66-7. t Ibid., pp. 64-6, 



% Nature, xxxix, (1889) pp. 259-61. 



