734 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of the visceral ganglia. The osphradium may be more or less widely- 

 separated from the visceral ganglion with which it is connected, as in 

 the Gastropoda, or quite close to it as in the Lamellibranchiata. 

 The second arrangement is the better for testing whether the nerve- 

 fibres which end in the osphradium arise from the visceral ganglion 

 itself or from the cerebral ganglion. Transverse sections through the 

 cephalic extremity of the visceral ganglion of Mactra show that some of 

 the fibres of the cerebro-visceral connective do not penetrate into the 

 visceral ganglion, but go outside it and directly to the osphradium, 

 into which no nerve coming from the visceral ganglion passes. The 

 osphradium, therefore, does not differ from the other sensory organs of 

 the MoUusca in the origin of its nerve-supply. 



a. Ceplialopoda. 



New Phenomenon of Cleavage in Ovum of Cephalopods.*— Mr. S. 

 Watase has a preliminary communication on a curious phenomenon in 

 the cleavage of the blastoderm of Loligo pealii. The ovum exhibits 

 distinct bilateral symmetry. In some preparations the nuclei in the left 

 half were found to be dividing, while those on the right side were at 

 rest, and in others the phases of activity were reversed. The author has 

 followed up the alternating phases of activity and rest in the two halves 

 of the bilateral blastoderm, until 116 segments were formed. The 

 phenomenon, whether pathological or normal, probably has some im- 

 portant bearing upon the problem of bilateral symmetry, and may 

 possibly throw light on the bilateral symmetry of form and function in 

 all its degrees of evolution. 



j8. Pteropoda. 



Anatomy and Histolog'y of Cymbuliopsis calceola.t — Mr. J. I. 

 Peck has had the opportunity of making serial sections of this Pteropod. 

 The muscular system is almost entirely limited to the regularly inter- 

 crossing separate bands that furnish the fin ; the outer layers of these 

 lie diagonally at the sides. Just within them there is a layer, the fibres 

 of which pass from oiie edge of the fin across to the other in arcs of 

 concentric circles. Still more deeply there is a layer of muscle-bands 

 that radiate from the proboscis to the margin. Each edge of the 

 proboscis is rolled outwards into two diverging folds that form a ciliated 

 groove leading to the large mouth. This is devoid of any remnant of 

 buccal armature or salivary glands ; mucous secreting cells are abundant 

 in the oesophagus ; the " liver " does not open into the stomach by any 

 proper duct, but by a single, wide, direct communication. The herma- 

 phrodite gland almost completely envelopes the visceral mass; the 

 accessory reproductive glands are large and much compressed into folds ; 

 the genital ducts are strongly pigmented and are ciliated throughout. 



In addition to the parts of the nervous system already described for 

 Cymhulia there is an additional commissure connecting the large pedal 

 ganglia. 



Systematic Position of Desmopterus papilio.:|:— Prof. P. Pelseneer 

 discusses the characters of this Pteropod lately described by Chun, and 

 placed by him in a new family of the Gymnosomata. It appears that it 



* Circ. John Hopkins Univ., viii. (1889) pp. 33-4. f T. c, pp. 32-3. 



X Zool. Anzeig., xii. (1889) pp. 52£-6. 



