858 SUMMARY OF CURRENT RESEARCHES RELATING TO 



oval cavities lined witli epithelium. The use of stronger magnifying 

 powers revealed masses comparable to young sperm-balls, in the form 

 of cells of the same size as the ordinary wandering cells, containing 

 several nuclei but no perceptible endothelium. Thinking that the 

 scarcity as compared with the ova of these bodies (which he hence- 

 forth regards definitely as male elements), perhaps indicated the exist- 

 ence of a relatively dioecious condition, he examined a large number of 

 specimens, and at last found a relatively male specimen, i. e. one in 

 which ova were scarce, but iu certain sections from which abundant 

 sperm-masses in all stages were found. From a comparison of these 

 stages, the author has drawn out what he considers to be the normal 

 course of development. The earliest stage is an ordinary wandering 

 cell, such as originates ova also, 0*008 to 0'02 mm. in diameter, with 

 transparent vesicular nucleus and strongly refractive nucleolus ; such 

 are further found containing two nuclei of difierent sizes, placed 

 at opposite poles of the cell ; next is found a " primitive sperm-cell " 

 inclosed in a " covering-cell," which Polejaeff assumes, although he 

 is not certain of the fact, to be derived from the two nuclei just 

 mentioned and the protoplasm surrounding them. The nucleus of 

 the primitive sperm-cell divides and subdivides — the protoplasm not 

 being seen to take part in this process until the mass enclosed by 

 the covering-cell is a number of very small strongly refractive 

 granules lying in completely transparent protoplasm ; the granules 

 probably give rise to the heads, the protoplasm to the tails of the 

 spermatozoa, but this again is not based on direct observation. The 

 further history of the capsule is unknown ; the sperm-ball does not 

 increase in size. The mature spermatozoon may be seen under a 

 power of 400 diameters, but usually only the round head ; to detect 

 the tail a section taken from the living sponge should be so treated 

 as to isolate the liquid containing the elements and the latter watched 

 as they die ; the head passes into the tail abruptly ; the latter has a 

 serpentine outline when death occurs, and appears to have a length 

 not exceeding • 03 mm. 



The differences between this mode of spermatogenesis in Calcarea 

 and that which seems common to Horny and Siliceous Sponges, 

 according to the observations of F. E. Schulze and others, are (1) the 

 non-division of the entire contents of the mother-cell into other cells, 

 a point which is probably merely relatively distinctive; (2) the 

 absence of an endothelium to the capsule, probably due to the absence 

 of that centrifugal pressure on the surrounding mesoderm-cells, which 

 the sperm-mass exerts in those cases where it increases in bulk ; (3) 

 the incomplete separation of the sexes. The great vitality of the male 

 elements is a striking fact, which may account for the great produc- 

 tiveness of this sponge ; spermatozoa have been found alive in half 

 decomposed specimens full of Bacteria and Infusoria. 



Fresh-water Sponges of Bohemia.* — Dr. F. Vejdovsky reduces 

 the previously published European species of Spongillidce to five, 

 viz. lacustris, jordanensis, fluviatilis, mulleri, erinaceus. He considers 



* Abhandl. K. Bobm. Gesellsch. Wissensch., xii. (1883) pp. 1-44 (3 pis.). 



