268 NATURAL SCIENCE. April, 1897. 



cuticular chitin. Due weight was given by some, at least, of the 

 recent writers in this journal to the reduction of the coelom and the 

 swelling out of the blood spaces as an Arthropod character — a 

 character to which the ' ostiate ' condition of the heart is clearly 

 related, and one which I believe I was the first to point out, together 

 with the related derivation of the tubular gonads from nephridia and 

 perigonadial coelomic remnants (cf. my note on Mr. Gulland's paper, 

 *' Evidence in favour of the view that the coxal gland of Limiilus and 

 of other Arachnida is a modified nephridium," Quart. Joiivn. Micr. Sci., 

 vol. XXV., 1885, p. 515). It is, however, to be noted, that a similar 

 (but not identical) reduction of coelom and enlargement of blood- 

 spaces occurs in Mollusca — and that if we take it alone, without 

 associating with it the resulting ostiate character of the heart, this 

 character is not distinctive of Arthropoda. It is interesting to recall 

 in this connection what was the most advanced teaching twenty years 

 ago, viz., that of Carl Gegenbaur. He states ("Elements of Com- 

 parative Anatomy," English edition, 1878, p. 278) that the coelom is 

 found in all the Arthropoda and " forms a portion of the blood- 

 vascular system, so that the peri-enteric fluid found in many Vermes 

 as a fluid different from the blood, is represented in the Arthropoda 

 by the blood itself." And similarly in the chapter on the coelom of 

 mollusca we find (p. 367), " As a rule, the vascular system is freely 

 connected with the coelom, which therefore forms a portion of the 

 haemal system." 



I think that it must be admitted that an important change has 

 been made in our views of the morphology both of Arthropoda and 

 Mollusca by the result arrived at some years ago through my 

 investigation of the coelomic and vascular systems of Mollusca and 

 Arthropoda (confirmed and established in the latter case by Sedgwick's 

 researches on Peripatus development), though that change is not so 

 widely recognised abroad as in England. Even that most distin- 

 guished anatomist, Kowalewsky, in a recent valuable memoir, still 

 calls the ventral blood-sinus of a hexapod insect its coelom. Many 

 morphologists, both in England and Germany, now recognise that 

 both coelom and blood-system exist in Mollusca and Arthropoda as 

 distinct systems of spaces shut off from one another, the coelom being 

 reduced to perigonadial, epi-nephridial, and (in Mollusca) pericardial 

 remnants, whilst the blood-vessels have swollen and united to form an 

 extensive series of blood-sinuses, to which I have given the name 

 " haemocoel." 



Oxford. E. Ray Lankester. 



