18 SUMMARY OF CURRENT RESEARCHES RELATING TO 



epidermis; the bony plates of the dermis ; the developmenl of the bony 

 plates, which is wholly due to the median and inner layers of the dermis ; 

 and the integumentary sensory spots. 



Nematocysts in various Groups.* — 0. H. .Martin publishes a note 

 on the occurrence of nematocysts and similar structures in the various 

 groups of the animal kingdom. He examines the evidence for the 

 occurrence of such structures in Protozoa, Sponges, Turbellaria, Nemer- 

 tinea. Mollusca, and Chordata. True nematocysts he regards as de- 

 veloped only in, and characteristic of Ccelenterates ; and he classifies 

 these, and structures in other animals which have been described as 

 nematocysts as follows: 1. Autocnidae : true nematocysts developed 

 singly in a true nematoblast within the tissue of its possessor (Ccelen- 

 terates. 2. Cleptocnidaa : Ccelenterate nematocysts which have been 

 ingested with* the food, and are found unexploded in the tissues of their 

 possessor (iEolids, Turbellaria, etc.). 3. Pseudocnidae : often confused 

 with true nematocysts, but not homologous. This group includes the 

 nematocysts of certain Nemertines from which a spiral thread can be 

 discharged ; those of Epistylis and Otoplana, in which the thread is not 

 preformed with the capsule, and those of Turbellaria in which no trace 

 of a thread has been discovered. 4. Polar capsules : strictly analogous 

 as regards development, structure and mechanism to true nematocysts, 

 but confined to a single group of the Sporozoa. The author points out 

 that if all these groups are regarded as homologous, their presence in 

 such isolated instances in various groups Would present great difficulties 

 to the evolutionist. If they are analogous and have been evolved afresh 

 in each case, they afford an amazing instance of what is apparently con- 

 vergent evolution. The problem of the nematocyst position — so that 

 when the thread is discharged it will pass out of the animal — is discussed 

 and possible explanations are suggested, e.g. that the nematocyst exercises 

 some stimulus on the cell which contains it, or, that the structure and 

 shape of a hydroid nematocyst will, mechanically, set it at a certain angle 

 under certain conditions of pressure, and that the resultant of these 

 forces leads to the nematocyst under the skin always pointing in the right 

 direction. 



C General. 



Plankton. f — J. Graham Kerr first discusses the adaptations of the 

 plankton. The macroplankton is illustrated by Medusae, pelagic 

 Annelids like Tomopteris, the Le/'tocejihalus-stage of eels. Among their 

 characteristic features may be noted the transparency (even haemoglobin 

 is suppressed in the Lpptocephaliis-st&ge), types of coloration which 

 harmonize with the environment, the frequency of photogenic organs, 

 the well-developed sense-organs, and the development of floats (like the 

 swim-Madder of' fishes). In the microplankton the problems of flotation 

 are different from what they are in the case of larger forms. The 

 natural rate of sinking of small bodies is very slow ; the viscosity of the 



* Biol. Centralbl., xxxiv. (1914) pp. 248-76. 

 t Buteshire Nat. Hist. Soc, 1914, pp. 1-9. 



