NOTES. 355 
like one of the ring-shaped air-cushions one sees, on a very small scale. 
Dr. Grobben describes the spermatoblastic cells of the testis and their 
nuclear spiudles ; but his account of the development of the spermatozoa 
does not agree with my own observations, which, so far as they have 
gone, lead me to infer that the annulate corpuscle of the spermatozoon 
is the metamorphosed nucleus of the cell from which the spermatozoon is 
developed. For want of material, however, I was unable to bring my 
investigations to a satisfactory termination, and I speak with reserve. 
Note XIV., CHAptTser IV., p. 174. 
THE MORPHOLOGY OF THE CRAYFISH. 
The founder of the morphology of the Crustacea, M. Milne Edwards, 
counts the telson asa somite, and consequently considers that twenty- 
one somites enter into the composition of the body in the Podoph- 
thalmia. Moreover, he assigns the anterior seven somites to the head, the 
middle seven to the thorax, and the hinder seven to the abdomen. 
There is a tempting aspect of symmetry about this arrangement ; but as 
to the limits of the head, the natural line of demarcation between it and 
the thorax seems to me to be so clearly indicated between the somite 
which bears the second maxille and that which carries the first maxilli- 
pedes in the Crustacea, and between the homologous somites in Insects, that 
Thave no hesitation in retaining the grouping which I have for many years 
adopted. The exact nature of the telson needs to be elucidated, but I can 
find no ground for regarding it as the homologue of a single somite. 
It will be observed that these differences of opinion turn upon ques- 
tions of grouping and nomenclature. It would make no difference to 
the general argument if it were admitted that the whole body consists 
of twenty-one somites and the head of seven. 
Note XV., CHapTer IV., p. 199. 
THE HISTOLOGY OF THE CRAYFISH. 
In dealing with the histology of the crayfish I have been obliged to 
content myself with stating the facts as they appear to me. The discus- 
sion of the interpretations put upon these facts by other observers, espe- 
cially in the case of those tissues, such as muscle, on which there is as 
yet no complete agreement even as to matters of observation, would 
require a whole treatise to itself. 
AA 
