232 SUMMARY OF CURRENT RESEARCHES RELATING TO 



accumulation of mesoderm cells, which gradually separates from the main 

 mass, and pushes the passive ectoderm outwards before it. The component 

 cells become large and round and extend dorsally, eventually forming blood- 

 corpusclcs. 



(c) The triangular germinal disc becomes distinctly marked. The apex 

 or posterior lobe represents the rudiment of the abdomen, the base or 

 anterior lobe that of the cephalothorax. Transverse furrows form the 

 segments and the appendages ajjpear as papilla-like protrusions of ectoderm, 

 into which the mesoderm also penetrates. The mesoderm is also segmented, 

 and the body-cavity appears as a cleft in each segment. Large round cells 

 near the somites form the blood-corpuscles. The ganglia begin to appear 

 as paired thickenings of ectoderm. Salensky's observation as to the two 

 semicircular folds in the head-lobes is confirmed. Soon the halves of the 

 germinal disc, and also the mesoderm somites begin to grow dorsally and 

 eventually meet above. The incipient blood-corpuscles collect in a dorsal 

 abdominal strand, and this is surrounded by mesoderm which thus forms 

 the heart. The stomoda^um and proctodfeum are formed as usual. A few 

 days before liberation, the scattered endoderm colls in the yolk separate 

 themselves from the latter at the internal ends of stomodnsum and procto- 

 doBum, forming two tubes which gi'ow together. These come into association 

 with the rudiments of the liver lobes. The respiratory sacs appear as two 

 ectodermic invaginations at the base of the first pair of abdominal append- 

 ages, which become their external coverings. The second pair of abdominal 

 appendages disajipear. The third and fourth pair form the spinning 

 papilla3 as Saleusky noted. Ectodermic invaginations form the glands. 

 The Malpighian tubes developc from two evaginatious from the proctodaeum. 

 Anatomy and Physiology of Glyciphagidae.* — M. P. Megnin finds 

 that the small cylindrical prolongation which has been described by 

 MM. Fumouze and Eobiu at the end of the abdomen of the female 

 Glyciphatjiis is an exclusively copulatory organ ; before copulation it is a 

 tube open to the exterior and communicating with a spherical pouch, which 

 is a true spermatic reservoir ; alter the act the opening of the tube becomes 

 obliterated, the pouch disappears, and the ova are laid by the subthoracic 

 genital organ, which has no other function. 



At times of starvation the young octopod Glyciphagi undergo a proto- 

 plasmic liquefaction of all the organs contained in the limbs and trunk ; 

 the gelatinous material is collected in the cavity of the thorax, and its 

 spherical mass becomes surrounded by a chitinous envelope. So long as 

 the circumstances persist, which led to this condition, so long it persists, 

 and the creature is like a grain of dust at the mercy of the wind ; put 

 under, or reaching more suitable conditions, development proceeds. Here, 

 we have the explanation of the sudden appearance of myriads of mites 

 which seem to have ajjpeared spontaneously. 



Anatomy of the Tyroglyphidae.l — Dr. A. Nalepa in his second essay 

 on the anatomy of the Tyroglyphidae, states that the chitinous covering is 

 generally thin and extensile ; where it is thicker it is friable and striated ; 

 the hypodermis is a plexus of ramified cells with rare nuclei, and tho 

 connective tissue has a similar structure. In the latter there is a quantity 

 of fat and carbonate of lime deposited, and here and there are colossal fat- 

 cells. The oil-glands are dermal organs, developed in shallow pits of the 

 epiblast on either side of the proctodaeum ; they are invested in a cubical 

 epithelium which secretes an oily fat. 



» Comptes Rcndus, ciii. (1886) pp. 1276-8. 



t SB. K. Akad. Wiss. Wien, xcii. (1886) pp. 116-67 (3 pis.). 



