880 SUMMARY OF CURRENT RESEARCHES RELATING TO 



creases in lengtli the larva takes on the form of a Cercaria; the 

 mesodermal cells of the tail are converted into spindle-shaped muscle- 

 cells, and the tail commences to exhibit its function as a locomotor 

 organ ; at the same time the mesodermal plates of the body of the larva 

 exhibit metameric segmentation. At this stage the provisional anterior 

 vesicle, which disappears as rapidly as it is formed, is developed. A 

 second vesicle is formed somewhat later between the body and the 

 tail ; its development divides the mesoderm of the larva into two 

 halves, one of which remains in the tail in the form of distinct muscle- 

 cells, while the other forms metameric plates on either side of the 

 body of the larva. During the whole time of its presence the tail 

 appears to undergo no change. The nervous system which, up to this 

 time, had extended throughout the whole length of the body, breaks 

 up into a hinder thinner and an anterior thicker part. The invagi- 

 nation of the ectoderm, to form the egestive orifice, pushes the hinder 

 part nearer to the long axis of the body, and this hinder part continues to 

 diminish in size through all the later stages of development, till it is 

 at last converted into the nerve which supplies the gill-lamellae and 

 the nutrient canal, while the anterior and thicker part gives rise to a 

 ganglion. 



The tactile cells are developed at a somewhat later period, and 

 the so-called auditory organ is, later on, formed from a battery of 

 the tactile cells. The gill-lamella is formed by the fusion of the 

 anterior and posterior invaginations of the ectoderm, and the clefts 

 begin to be formed before the muscular bands are completely differ- 

 entiated. The rosette-shaped organ is formed by four outgrowths of 

 the endoderm of the ventral surface, which are met by corresponding 

 invaginations of the ectoderm ; the former, in coiirse of time, becomes 

 separated from the rest of the endoderm. The mesodermal plates 

 give rise to muscles, and the heart, with the pericardium and blood- 

 corpuscles. After all the organs of Doliolum are more or less developed 

 the tail begins to undergo atrophy ; muscular contractions bring 

 about a closer apposition of the chorda-cells, the tail gets shorter, 

 the ectodermal vesicle smaller, until at last all sign of the appendage 

 completely disappears from without. Within, a cell-mass formed of 

 chorda-cells, with smaller muscle-cells imbedded in it, and presenting 

 a resemblance to the elaeoblast of the Salpte, is for a short time present. 

 When the tail disappears, the muscles begin to exhibit activity, and 

 soon, the egg-covering disappearing, the larva is set free. 



Celleporse from the 'Challenger.'* — Mr. Busk describes 27 

 species of Celleporce believed to be new, collected by the ' Chal- 

 lenger' Expedition. The figures, which are of great importance 

 in this difficult genus, will appear in the official Monograph of the 

 ' Challenger ' Bryozoa. One species was brought up from a depth 

 of 2600 fathoms in the Australian region, and another from 1325 

 fathoms in the South Pacific, but Mr. Busk says that, on the whole, 

 the genus as represented in the present collection would appear to 

 belong to comparatively shallow water. The author divides the 



* .Tomn. Linn. Soc. (Zool.) xv. (1881) pp. 341-56 (4 figs.) ; ib. pp. 357-62 

 (2 pis. and 7 figs.). 



